They're West African Crocodiles, not Nile Crocodiles. A smaller and much more docile species.

Not that they aren't dangerous, they are known to attack and have killed people from time to time, but there's a long history of humans handling them - sometimes literally - in ways that would be considered suicidal if attempted with Nile crocs. Even going as far back as Pharaonic Egypt people knew there was a difference between the two and knew which one they'd rather get close to.

The US military in WW2 was still segregated - black soldiers were primarily used as labor, not as combat troops.