W/a little research I was able to determine that freewheel cogs had been developed by this time period, so at least they didn't have to attempt this ride on fixed-gear bikes. Haven't been able to find out whether the 3 sp igh or derailleur had.

All the bikes are equipped w/full coverage chainguards, so it's doubtful re a derailleur system. Most likely a freewheeling single-speed. One piece cranks? I'd venture something like 42x18-20. It's hard to tell from the pics whether the bikes have coaster brakes or calipers.

Man, w/all the food and equipment each soldier had to carry? And things weren't light in those days. Canvas tents and wool uniforms? Wow. Incredible accomplishment.