auxiliary vessel
A naval term for a support ship that is not a front-line combat vessel, such as a supply ship, repair ship, or tug.
Auxiliary vessels carry supplies behind the fleet.
戦闘艦 is a combat vessel, while 補助艦艇 is a support vessel.
Compound of 補助 (ほじょ, 'auxiliary, support') and 艦艇 (かんてい, 'naval vessel').