they wear?

kind of like a long apron that covers them from chest to groin.

Any idea what they were made of? They look thin.

Nothing like modern equipment.

Early bulletproof vests, like those seen in shows such as "Adam-12," were often made from materials like silk or cotton, which were layered to provide some level of protection against low-velocity bullets. These vests evolved over time, incorporating stronger materials like Kevlar and ballistic nylon for better defense against modern firearms. Wikipedia hwinbulletproof.com