"Our all-transgender brigade has suffered heavy casualties!"
"What? We haven’t even sent them to fight!"
"They’ve already lost 30% of the unit!"
Transgender Brigade Casualties
Explanation
Explain Bear
Listen up, buttercup. This joke is all about wordplay and assumptions. The punchline reveals the "casualties" aren't from battle, but from transitioning i.e. losing members of their unit as they become women.