Armor

How much armor to stop a sword?

First, it depends on how strong the person hitting you is.

Let's assume they're a stout fellow with a ST of 12.  This is also a common ST for a character expected to do hand-to-hand damage.

Next, it depends on what kind of sword...

GURPS is wonderfully concise about swords.

Nearly all single-handed swords are covered by "broadsword"

The bog-standard "broadsword" has a fairly blunt tip and is more of a straight edged cutter.

The tip gets sharper as armor gets better, becoming very pointy indeed before changing over to what we'd think of as a rapier.

Just to let you know how broad GURPS is with broadsword, the following weapons are all "broadswords"!

Khopesh

Broadsword

Large Falchion

Pata

Shotel

Bastard Sword (used one handed)

Dao

Estoc

Hook-Sword

Jian

Katana

Longsword

Backsword

Cavalry Saber

Edged Rapier

They are all used similarly. 

But how much to stop one?

ST 12 with a standard thrusting broadsword gives 2d-1 cut and 1d+1 imp.

So, on average, someone with DR 6 is immune to a sword most of the time.  DR 11 to be completely impervious.

It's not easy to get to that high DR, not until aramid fibers and ceramics.

Just protecting your torso (front and back) from this is heavy (and expensive).  TL2 is iron age.  TL3 is medieval.  TL4 is Renaissance.

TL2 heavy mail gives DR 5* and is 18 lb.  $1,200.  -2 DR against crushing.

TL3 Jousting mail gives DR 6 and is 30 lb.  $1,500.  -1 DX except for Lance Skill.

TL4 medium plate gives DR 6 and is 20 lb.  $2,500.

TL4 heavy plate gives DR 9 and is 32 lb.  $4,000.

You can spend less and get less protection.  Often you can pay less for the same protection with a weight penalty.

To get DR 11 at TL3 (which we think of as typical Fantasy) you need to layer your armor with its attendant -1 per layer DX penalty.

Heavy chain worn under a bronze medium plate gets you there.  DR 11 and 38 lb. for $11,200!

For Henry VIII at TL4 it doesn't weigh any less, but you save money now that steel can be used for the corselet.  $3,700.

The king, though, would have hardened steel armor, or duplex plate.  Fine mail under medium plate with hardening gives DR 12, 35 lb. and $17,000.  Upping the plate to duplex is still DR 12 but 33 lb. and $27,000.

You can also make what plate you have heavier (Low-Tech p.109)

TL2 Heavy segmented plate starts at DR 5, $1,200 and 32 lb.  Cranking it to DR 11 goes to $4,800 and 128 lb!  But you don't take a DX penalty...

And that's JUST your torso.  Each arm is 25% of that.  Each leg is 50% of that.  Each hand and foot is 5%.  So 2.7 times the torso costs and weights to get a complete suit. 

Just for the record, historically, absolutely NOBODY wore the maximum armor technologically possible to the field.

Also for the record, proofed armor is DR 9, the same as TL4 heavy plate.