The 5th Fleet Security were troopers that were in charge of keeping security on Republic ships. And if there were few pilots on the ship during a battle they would fight in space combat. They were also known to be military police on ships.
During the Clone Wars, the 5th Fleet Security utilized Phase I clone trooper armor and later in the war, Phase II clone trooper armor. Their armor sported blue lines across the helmet, torso and thigh. The 5th Fleet Security also had an elite brand of clone commandos. Some clone commandos wore white armor with blue, and some wore black armor.