The Bell UH-1 armed helicopters operated by HA(L)-3 were, in most respects, straight line Army machines. Temporarily surplused from the Army inventory, these helicopters had usually already seen a lot of long and hard use. Those received directly from the Army units in Vietnam most often required a good deal of repair and rejuvenation before being sent out into Naval service. Others received from the Army's overhaul depot in Corpus Christi, Texas, were generally in much better condition. "Navalizing" these helicopters was relatively simple involving addition of the specialized door gun mounts and a radar altimeter. The radar altimeter was a crucial piece of equipment, for operating over the flat delta terrain in bad weather, at night, in the absence of a good horizon reference, required precision altitude indications. This was especially true when recovering aboard the support ships at night as landing aids were very rudimentary. A shortage of radar altimeters plagued the squadron for many months so that they were rationed to those dets which operated off the boats, and even then it was not unusual to find only one helicopter in a det with this specialized instrument.  (source: www.seawolf.org )