World War 1 combatives...what fun!
I found a youtube video depicting World War 1 combatives. Looks like boxing and classical jujitsu. You can tell how the boxing is old school because the guard is down, and they seem to be practicing a lot of straight punches to the gut as counters to high punches, whereas nowadays boxers would generally prioritize countering to the head whenever possible. If you watch the whole thing, there's a short segment where you see hand to hand combat with chem gear, that involves a gas mask rip.