Traveller has, from time to time, taken a little gentle ribbing over the fact that it has rules for spears and swords. This is a game of science fiction adventure in the far future. Well, so what if it does? Sci-fi classics from The Time Machine to The Dumarest Saga and King David's Spaceship had characters use swords and other melee weapons.
So there should also be rules for the use of that natural companion of the sword, the shield.
Shields are the oldest defensive technology of mankind. A shield is a portable barrier, often strapped to the arm or carried by one hand. It protects the bearer against attacks from the front.
Normally you use a shield with a one-handed weapon (blade, club, handgun). If the bearer wishes, he can fit his shield with a weapon rest so that the shield supports long arms (spears, long guns). All attacks with these weapons are at DM -2. Very high-tech shields may incorporate stabilization and anti-grav to negate this penalty. Imagine heavy weapons carried behind a gun shield!