Slaved To The Gun

Some write ups comparing the fire control of the M60A3 and M1 make it seem like there's no reason to use the M1 fire control system.

Both are fully stabilized.

Both use laser range finders.

Both have wind sensors.

Fruit, fruit.  Tits, tits.

The M1 computer has more processing power and does the job faster, but it doesn't make a big difference when the time choke-point is the loader. 

The gun is slaved to the sight.

What this means is when I'm tracking a target and stab the lase button, my view, and the crosshairs stay on the target and the turret shifts.

But what makes the M1 system better?

In a word, integration.

The M1, and it's fire control computer, were designed together.

The M60's system is an add-on that had to work with existing hardware and that makes it a bit clunky.  This article gives a decent description. 

RPG Pen

If you look closely, you'll see a small hole under the smoke-grenade stowage box.

We had a HEAT round battle carried and we were pieing the corner of an alleyway when we got hit. I thought they got a 1:1mil shot down our gun tube at first.

I was the loader. My gunner and TC both got peppered pretty well from the blast and I caught a bit as well.

Gunner got medevac’d to Germany because of the flash burns to his face. “Ruined his modeling career” as he put it.

The hole in the sponson box was actually from an earlier rpg attack, but it hit sandbags in the box and never detonated.

The small hole at the lower left side under the smoke grenade box is the entrance hole of the one that did us in.

Plt Sgt had me digging in the hole with needle nose pliers trying to get something out when Col. Robert Abrams (our Brigade Commander at the time) walked up and said “what the fuck are you doing?!?” Good times.”

-- David S

The write up explains it's an M1A2SEP.

That makes the side turret DR 1,580L.  1,147mm RHAE v HEAT.

For a heat round to penetrate that it needs to be, at least,  6dx15(10) cr ex, for the average hit to penetrate.  6dx9(10) cr ex can penetrate with a max-damage roll.

The PG-7VR warhead can penetrate 900mm of RHA with its tandem warhead.  At first you think it cannot, but the damage roll is based on an average where all the dice roll 3.5.

I'm not showing all my work here, read the rules and it's clearer. 

6dx4(10) cr ex follow-up 6dx8(10) cr ex linked 6dx5 cr ex; which is treated as a single 6dx12(10) cr ex attack if there is no reactive armor.  On average it penetrates DR 1,260L

So, DR is doubled for laminated armor vs HEAT.  3160.

Divided by the armor divisor of 10.  316.

Divide by 12 to find out if we can penetrate with this round, if it's more than 36, no.  26.3333.

The PG-7VR, on a good roll, can penetrate the turret side of an M1A2SEPv1.

This GURPS.

Who Would Win

I've noticed that the Soviets had better guns and thicker armor than the NATO nations until relatively late.

NATO didn't start getting gun parity until the British 105mm L7.

NATO didn't start pulling ahead in armor until Chobham.

NATO tanks are almost always taller and heavier than their Soviet counterparts.

So, NATO was screwed before tanks like Abrams and Leopard II hit the scene?

Maybe not.

For the gun and armor to matter, you need to hit, and the Western designers put a lot of effort and thought into fire control.

The first step in accurate fire is an accurate determination of the target's range.

You'll see little bulges on the sides of US tank turrets.  These hold the objective lenses of the range finder, either coincidence or stereoscopic.

The earliest of these give the range which is called out and the appropriate stadia in the optic is aligned with the target.

The US miniaturized the mechanical fire control computers it'd been using on ships and put them in tanks.  The range obtained from the rangefinder could be input into the computer, along with wind speed and the reticle would be shifted so the gunner need only align a, relatively simple and uncluttered, crosshair on the target to hit.

This is all happening while the T-55 has no rangefinder at all and the T-62 uses stadiametric ranging.

The US then automated the process by putting a linkage between the rangefinder and fire control computer.

This was in the 90mm equipped M48A2, in 1953!

The M60A1 started with this.  Later versions got a solid state computer, laser rangefinder and sensors to compensate for wind muzzle droop and cant.

This is all in addition to stabilization that allowed for firing accurately on the move.

Of course, to effectively use all this fun technology requires some education and training that's, typically, absent from the Warsaw Pact and Soviet customers.

Israel vs et al kind of proves the thesis. 

For Comparison's Sake Gun Stats Update

Updated from this post. 

GURPS: World War II has stats for WW2 vehicles, surprisingly enough.

Since I've been mentioning the performance of Cold War stuff, and many people are more familiar with WW2 shit...

It's Front/Sides/Back/Top/Bottom (if needed)

Sherman M4A1 Hull: 300/150/150/75/50; Turret: 300/200/200/100

Gun Motor Carriage M10 Hull: 255/85/85/55/50; Turret: 275/100/100/0

Panzer IV Ausf H Hull: 315/120S/80/40/40; Turret: 200/120S/120S/40

Panther Ausf G Hull: 540/190S/160/60/120; Turret: 600/260/260/60

Tiger Ausf E Hull: 400/420/320/100/100; Turret: 425/310/310/100

Königstiger Ausf B Hull: 850/310/310/155/100; Turret: 700/310/310/170

T-34/76 1940 Hull: 350/250/175/75/75; Turret: 350/250/175/80

Guns!

M4A1 Sherman's M3 75mm firing the M61 APCBC or just AP does 6dx6(2) pi++.  That's good for a whopping 252 DR.

The "long 75mm" 76mm M7 cannon firing M62 APCBC delivers 6dx12(2) pi++ and a linked 6dx2[4d-1] cr ex.  This punches 504 DR.  M93 HVAP does 6dx12(2) pi++ without the linked explosion and punches the same 504 DR  This was considered HOT ammo!

The 7.5cm KwK40 L48 on the Pzkw IV-H firing a PzGr 40 APCR or APHC does 6dx12(2) pi++ that will penetrate DR 504 with most dice.

A KwK42 7.5cm on a Panther G lobbing a PzGr 40/42 does 6dx14(2) pi++.  That's good for punching holes in DR 588.

Tiger E's KwK36 8.8cm gun gets the most penetration with the PzGr 40 which is an APHC round doing 6dx13(2) pi++.  That'll punch 546 DR on average.

The heavier Tiger II's KwK43 8.8cm gun shooting a PzGr 40/43 round gets 6dx16(2) pi++ to routinely stab through 672 DR.

The pride of the Soviets 76mm L-11 gun firing BR-354P APHC does a mere 6dx9(2) pi++ for an average penetration of 378 DR.  And people were bagging on the M3 in the Sherman!

Update: The D-5T 85mm gun from the T-34/85 firing a BR-365 APHEX round will do 6dx13(2) pi++ with a linked 7d+1[4d+1] cr ex.  That will penetrate 546 DR on average.

As a reminder, the 90mm gunned M48A3 has Hull: 606/314/96/113/87; Turret 716/314/281/129; Cupola: 386/386/386/193.

The M41 gun firing M332A1HVAP APHC does 6dx12(2) pi++ for 504 DR penetration.  Not enough for a lot of the heavy Nazi armor.  Damn the Tiger II is tough!  The Patton is somewhat vulnerable to the King Tiger's gun, but it's even more mobile than the Sherman that maneuvered around it to get rear shots.  But HEAT is what we thought would be the real armor puncher.  The M348 HEAT round does 6dx4(10) cr ex with a linked 6dx 3 cr ex that will burn a hole in 840 DR.  The hull front of a Königstiger is still not penetrated!  But the more visible turret front is!

However its expected opponents the T-54/55 and T-62 aren't near so well protected, but they're a lot more mobile:

T-55: Hull 330/218/165/68/55; Turret 565/358/165/165

T-62: Hull 281/218/126/85/55; Turret 667/421/110/110

Good thing the Patton is mobile and reliable.

The 100mm D-10T firing a BR-421D APHEX round in 1953 does 6dx17(2) pi++with a linked 5d+1[5d] cr ex.  That will punch DR 714.

A 115mm U-5TS firing a 3BM4 APFSDS round in 1963 will do 6dx28(2) pi++.  That gets past 1,176 DR.  Yes, the Soviets were ahead of us on tank guns.

But what if we drag an M60 into the argument with its M68 cannon?

The 1959 issue M392 APDS does 6dx23(2) pi++ for 966 penetration.  The M456 HEAT will do 6dx5(10) cr ex with a linked 6dx3 cr ex and make a 1,050 DR deep hole.

 

Stronk

I have been operating on the idea that ST for mounted cannon didn't matter.

Otherwise the average character isn't going to be able to use them.

p. B270 backs this idea.

But I noticed that vehicles have a ST value.

Is your tank strong enough for the cannon?

There aren't rules as written for this, but I can see several ways of using it. 

Oh My God

Linky

During a routine inspection in 2026, museum staff uncovered a shocking secret hidden inside a WWII Panzer III tank that had gone unnoticed for more than 80 years. Beneath an internal floor panel was a 7.92×57mm Mauser round, the same ammunition used by the German MG 34 machine gun mounted on the legendary armored vehicle. The discovery stunned experts because the aging bullet was potentially dangerous and had to be carefully deactivated before being added to the collection. This rare Panzer III, one of only two surviving examples still running, carries a mysterious history dating back to the North African campaign and the Battle of Alam el Halfa in 1942.

So, a live round was rolling around under the floorboards for 84 years, and the lack of men in the UK caused a panic?

Potentially dangerous?

Maybe if you tried to swallow it.  It's not like it's an HE round where the explosive's stabilizers have been slowly breaking down leaving something behind that makes nitroglycerine seem easy to juggle.

I love the line about carefully deactivating it.

In America a quick poll would have been taken among the workers to see who had a 98k and they'd have shot that round to see how badly the powder had degraded. 

"Historian Ian Hudson said he could not definitely say the round was a wartime artefact but “it’s certainly very likely”." 

Are you fucking shitting me, Ian?

A fucking historian doesn't know to look at the headstamp?

I am ever more convinced that we should have helped the Germans in 1918. 

Odd Problem To Have

I'm doing Russian tank rounds now.

American rounds it's easy to find the weight of the loaded round, but hard to find the length and weight of the projectile.

Russian rounds have been the opposite.

Extensive data on the projectile, not much for complete rounds.

Of course, it's better than Nazi German ordnance, you can often find precise data on penetration values and be left wanting for how much anything weighs.

I am dreading doing France and the Brits. 

FFS Ordnance Bureau!

When the Army realized that the M2 and M3 guns in the M3 and M4 tanks weren't going to cut it for most anti-tank purposes...

OK, they didn't.  The M2 and M3 guns do exactly what they were supposed to do, and the Gun Motor Carriages were supposed to handle the stuff that was too heavy for the tanks.

So they made what we call "tank destroyers," or gun motor carriages.

The TD counterpart to the Sherman is the Gun Motor Carriage M10.

It's got a long 3" gun that's tailored to kill tanks.  This is the M7 gun on an M5 mount.

Towards the end of WW2, they started to replace the M10 with the Gun Motor Carriage M18 "Hellcat".  It too has a long 3" gun that's tailored to kill tanks.  This is the M1 series of guns.

The tank destroyer concept started to wane after the war and we developed a light tank with a long, 3" gun that had a decent chance against a tank.  This is the M32.

They all use the same round, right?

No.

No, they do not.

Despite all sharing the same caliber, they don't share the same case.

Frustratingly, The M7 and M1 guns share projectiles.  The cartridges are named after the projectile so they share designations.  76mm HE M42 for the M7 is a different round from the 76mm HE M42 for the M1.

The M7 gun fires 76.2x585mmR.

The M1 series fires 76.2x539mmR.

The M32 fires 76,2x580mmR.

The manuals that ordnance issues doesn't really distinguish between the 76mm rounds and even forgets there's more than one cartridge length.

What caused me to notice was going through the rounds for the Lee/Grant and Sherman's 75mm M2 and M3 guns.  Those guns both fire 75x350mmR.

But Ordnance doesn't specify that the 75mm Pack-Howitzer rounds are not the same.

The round that started my noticing was the 75mm M66 HEAT-T round and seeing how low the muzzle velocity was compared to other rounds fired by the Sherman.  Even lower than the shorter barreled gun in the Lee/Grant.

This is because the pack-hog fires 75x272mmR!  It gets a couple of rounds that the Sherman never got because it stayed in service a lot longer. 

It's getting sorted.

I have also made my first set of stats for a NBC round.  The M64 Chem round.  Mustard gas!  Not to be confused with the M64 Smoke and M64 HC Smoke rounds.

Bet They Were Feeling A Little Inadequate

The 8.8cm KwK.43's Pz.Gr.40/43 will do 6dx16(2) pi++ out to 5,950/17,500.

That's got more reach than the same projectile from a Tiger E.

The 8.8cm KwK.36's Pz.Gr.40 will do 6dx13(2) pi++ out to 4,980/14.600.

Those punch 9.6" and 7.8" of RHAE respectively.

The 90mm gun on the T-26 firing a M82 APC-T round does 6dx10(2) pi++ follow-up 6d+2[4d-1] cr ex.

That punches 6" of RHAE.

That's our best armor piercing round.

On the plus side, the Tiger II only has 5.9" of armor on the front of the hull.  That should only be DR 400, but it's sloped for DR 850 and the M82 round will ping...  You need 6dx21(2) to get a Tiger from the front.  We didn't develop a round that could do that until we filed the serial numbers off the Brit L7A1 105mm gun and called it M68.

On the down side, the T-26 firing that 90mm round almost has 4" of armor...  It too is well sloped and gets DR 420.  6dx10(2) penetrates that.

On the gripping side, there were damned few cats of any flavor running about when the T-26 arrived to test out the idea of what would become an MBT.

Done?

I have used Gun Stats to make stats for all of the US issued 90, 105, and 120mm tank gun rounds.

Yes, I remembered the M58 gun on the M103 heavy tank.

75 and 76mm beckon... 

Then it will be time to do the Soviet stuff. 

US Cartridge 105mm APFSDS-T M900

My old stats for the M900 were:

6dx34(2) pi++ inc; 6,000/18,000 - That's good for punching 518mm of RHA at 0°.

Gun Stats gives:

6dx33(2) pi+ inc; 8,140/26,700 for APFSDSDU.  503mm penetration.

6dx39(2) pi+ inc for long-rod APFSDSDU.  594mm penetration.  "Long-Rod" is defined as a penetrator being 15 times longer than its diameter.  The M900 penetrator is 25x603, 23 and change to 1.  It's a long-rod.

A bit short of both benchmarks I found back in Feb '25.  The round's performance is still classified (sorta) so there's not a lot of official information, but a great deal of "already leaked" information.  War Thunder thinks 522mm.

But 6dx39 is in the ballpark of what I think it should do. 

It's a game, so the important thing is the relative values come out about right even if the precise numbers don't quite.  Gun Stats even has a section about how to use stated penetration values to determine damage.

Take the RHA penetration in mm * 0.787 / armor divisor and that gives dice.  6dx34 in the case of 522mm!  But, like I said in Feb '25, I think it punches more, so I'm going with the long-rod numbers!

110 Years

110 years ago at The Somme, the tank made it's combat premier!

Seconds later, a tanker asks a crunchie an infantryman to hand them something they'd dropped to the ground because "death before dismount!" 

Wrong Designation

While I was restricting myself to things that were plausible for Twilight, I'd missed that the hoary old M577 stopped being M577.

Neatly sidestepping becoming the Mobile Command Post of Theseus the M577A2 was extensively upgraded and modernized to become the M1068.

A similar upgrade makes the M577A3 into the M1068A3.

Still looks the same on the outside and you'd be forgiven if you mistook one for another.

The M1068 is due to be replaced by the Bradley based M1286.

I once had a player group in one of my first conversions of T2K to GURPS select the M577A1 CP because it had air conditioning. 

Just A Couple Years Late

Twilight: 2000 had a few variations of the M2 Bradley which were projected to enter service, but never did.

It was a logical progression that the Brad would be modified as the M113 had and would have as many specialized variants.

Well...  No.  Especially with the Berlin Wall falling and ruining the chances we'd have full on nuclear combat, toe to toe with the Ruskies.  It also makes T2K an alt-history instead of a speculative future.

Darn.

It does turn out that the M113 is obsolete and not viable for frontline operations any more and that we needed something to replace all of its numerous variations.

Which we started to do in 2018 with the Armored Multi-Purpose Vehicle program. 

T2K's M18 mortar carrier is the real world's M1287.

The world only took 32 years to catch up to a game... 

Complete Or In Parts

Several places describing protective masks are including the complete kit in the weight and not breaking it apart into component parts weight.

For example:

The M25 mask includes the mask, hood, carrier, decontamination kit and atropine set.

TM 3-4240-280-10 says 6.25 lb with carrier, but no mention of the decon or atropine.  Since the filter is attached to the carrier in the M25 mask, it makes sense to have it be 6.25 lb.

I mean, that's what I was issued, but that's not my natural way of showing it on a character sheet.

A T2K Staple

I first read about the LAV-25 in a Popular Mechanics article on the Rapid Deployment Force.

Back then, the Army was still in on the project.

Because of that, GDW included it in Twilight: 2000.

It is, by far, the vehicle my players had most often.  Vagaries of the dice, I guess.

So here's a video about it!

Captain Vulnerable

 

Armor Coverage

Hit Locations

Captain Vulnerable gets his name from an image similar to this one for hit locations in Champions.

This is the GURPS 4e version and shows the hit locations from The Basic Set.

Low Tech changes the coverage for armor.

Skull (hit locations 3-4) remains the same.

Face (hit location 5) remains the same.

Legs (6-7 for right leg, 13-14 for left leg) change.  You get Thighs (5-6), Knees (4), and Shins (1-3).  For arm and leg hits, roll 1d and the result shows you where on the limb the blow strikes.

Arms (8 for right arm, 12 for left arm) change.  You get Shoulders (6), Upper Arms (5), Elbows (4) and Forearms (1-3).

Torso (9-10) changes.  First it becomes areas 9-11 then Chest takes over locations 9-10 and Abdomen takes over 11.

Groin (11) changes.  Groin is covered by Abdomen, but is given it's own location because you can armor JUST the groin.

Hand (15) remains the same.

Feet (16) remain the same.

Neck (17-18) remains the same.

Vitals are covered by Chest, but can be armored separately.

If you look at Capt. Vulnerable, you will see that torso coverage includes the shoulders.

Lots of armor doesn't in real life.  The M12 vest and the Ground Troops Variable Armor don't.

That means I need to remember to note "shoulders" when they have such coverage.

It's also striking how few flak vests have abdomen coverage.

PS: The illustration from 3e was clearer.

Issued Before It Was Type Classified

You'd think that a piece of gear designated M1969 or M69 would see its first issue not before 1969, wouldn't you?

Well, you'd be wrong in this case.

Armor, Body, Fragmentation Protective Vest with 3/4 Collar was first fielded in 1962 and gets continually tweaked until they finally settle on type classifying it as Body Armor, Fragmentation Protective, Vest with 3/4 Collar, M-69 in 1969.

First it had no stiffeners.  Then stiffeners were added.  Then they replaced the zipper (and pocket snaps) with velcro.

The stiffeners were added to keep the ballistic nylon innards from bunching up and leaving the upper part of the torso unprotected.

Trends

While I'm doing the Great GURPS Body Armor list...

I've noticed a trend in several nations and how body armor gets used.

First it becomes available, but not widely issued or used.

Then it becomes widely available, but neither issued or used.

Then it becomes widely issued, but left behind in the barracks.

Then it becomes accepted by the troops who nearly always wear it.

In the Korean war we had enough vests to equip all of our combat arms troops.  Hardly any units issued any vests.

In Vietnam, there was plenty of body armor to go around, but only the Marines insisted the troops wear it.  Most M69 vests sat under the bunk of the soldier they were issued to. 

For the US, troop acceptance and near universal use of body armor starts with the PASGT gear.

The common phrasing of "hot and uncomfortable" disappearing from the description of the armor correlates well with troops wearing the armor more. 

That's Handy

I was surprised to learn that the US Army developed and issued body armor for infantry in 1945.

Just in time to miss combat.

This was the Armor Vest, M12.  It's aluminum plates mounted like ship sails in brigandine fashion in a canvas carrier.  It was exported and Turkey used it in Korea.

The US also issued flak vests in Korea.  The M1951, M1952 and M1952A vests were all issued, first to Marines then to Soldiers.  These vests are very similar to one another in appearance but differ in construction and materials.  The M1952A is the first US vest to have no rigid materials as protection.

The Marines and Army diverge for Vietnam.  The Marines going with the M1955 vest and the Army the M69.

Making GURPS stats for these means I've also made stats for many other nation's vests because they got our vests as military assistance.

Notably Britain, who issued the M1952A and M69 to troops in Northern Ireland.

I'm a bit surprised that a book that I've owned for years has been more useful than the internet.