Parachutes were not used until WWII because in WWI planes were new and they were afraid that if pilots had the option of the parachute that they would be more likely to use them when they could land the plane safely instead. They wanted to avoid loss of plane, which were still fairly new and expensive. Since parachutes were used in WWII, we started out our WWII games with them.
We also talked about the use of camouflage, and played hiding games so they could see how much harder or easier it is to see someone depending on how much they blended into the background.
We made paper tanks. Although tanks have been used for years(DiVinci sketched plans for them!), the distinctive look that we are used to was first used in WWII.
We also looked at bombs a lot. We experimented with the physics of bombs. We made Vinegar and Baking soda bombs. We played a mine game.
After the long battle with water bombs, my soldiers had a soldier's lunch, complete with dried foods and "lollies" (an English term that is short for lollipop, and actually means any kind of hard candy, which was given to soldier because the stood up to heat and gave the soldiers quick sugar energy.)