Complex sentence: The "Summer" grill offered no protection for the radiator but by the time they were installed it was realized that the vehicle was expendable once it got the fire team to the fight, or the convoy being protected out of one.
Split into simpler sentences: The "Summer" grill offered no protection for the radiator but by the time they were installed it was realized that the vehicles were expendable. They realy did not need the protection, because they only had to survive long enough to get the fire team to the fight, or the convoy being protected out of one.