In a recent Warship Wednesday (Coast Guard Ron Three) we touched on the use of the 81mm mortar in two fixed emplacements behind the main 5-inch gun mount on a series of USCG cutters that deployed to Vietnam between 1967 and 1972.
The 81mm mortar was mounted on either side of the No. 1 (5-inch) mount, seen here on USCGC Campbell in 1967.
Developed by the Navy and Coast Guard in two different models (Mark 2 Mod 0 and Mark 2 Mod 1) in the early 1960s, the thought behind such mounts was that they could be used for illumination quicker and easier than shooting star shells from the main gun (which also could conceivably leave the main gun slow to switch gears from lofting illum shells to hitting surface/shore targets with HE).
Plus, the mortars could be used for near-shore naval gunfire support as well.
Campbell’s mortar team “hanging an 81” ashore
These mortars were also used extensively by the USCG’s 26 82-foot Point class cutters as part of CGRON One during the war, typically piggybacked with an M2 air-cooled Browning .50 cal BMG.
Rel. No. 6135: USCGC POINT LOMAS FIRED AT SUSPECTED VIET CONG CAVE HIDEOUT: An 81mm mortar shell fired from the 82-foot U.S. Coast Guard Cutter POINT LOMAS (WPB-82321) shatters rocks over the entrance to a suspected Viet Cong cave hideout along a beach in a Viet Cong controlled area near Danang. Rounds from a .50 caliber machine gun, mounted piggyback on the mortar gun also were fired into the cave. Commanding the POINT LOMAS is Lieutenant Keith D. Ripley, USCG of Baltimore, Md. The 82-footer was stationed at Port Aransas, Texas, before reporting for duty with Coast Guard Squadron One’s Division 12, based at Danang, Vietnam, in July 1965.
The Navy also heavily used them on just about everything that moved that was smaller than 165 feet in length, as detailed by Bob Stoner GMCM (SW) Ret. over at Warboats.org.
Navy 50-foot coastal patrol craft (PCF); Navy 75-foot fast patrol boats (PTF, “Nasty”-class); Navy 95-foot fast patrol boats (PTF, “Osprey”-class); Navy 164-foot patrol gunboats (PG, “Ashville“-class); miscellaneous riverine craft which were mostly converted LCM-6 landing craft: MON (monitor); CCB (command and control boat); Zippo (flame thrower boat); ASPB (assault support patrol boat); HSSC (heavy SEAL support craft); and advanced tactical support bases such as SEA FLOAT/SOLID ANCHOR (Nam Can) and BREEZY COVE (Song Ong Doc).
Cam Ranh Bay, Republic of Vietnam. Gunner’s Mate Second Class Robert Phalen, left, and another crewmember of Fast Coastal Patrol Craft 42 (PCF 42) prepare to fire an 81mm Mortar while on patrol, 18 October 1968. 428-GX-K60314
South Vietnam. Engineman Second Class McCune drops a projectile into a mortar on the deck of the fast coastal patrol craft (PCF-3) of Coast Division 11 as Boatswain’s Mate First Class Byerly stands by to fire on the Viet Cong unit position. Photographed by F. L. Lawson, 17 July 1967. 428GX-K40159
GMCM Stoner:
The mortar itself is mounted on a very robust tripod and uses clamps to control traverse and elevation angles. Unless fitted with NO FIRE zone mechanical stops, the mortar has 360 degrees of traverse and -30 degrees of depression, and +71.5 degrees of elevation. Its rate of fire is 18 rounds/minute at 45 degrees elevation in DROP FIRE mode and 10 rounds/minute in TRIGGER FIRE mode. Sights for the mortar are attached to the left side of the elevation arc. The weight of the Mk 2 Mod 0 was 593 pounds; the weight increased to 677 pounds in the Mk 2 Mod 1 (with machine gun). The range of the 81mm (direct) was 1,000+ yards; (high angle, indirect) was 3,940 yards. The maximum effective range of the .50 Browning machine gun was 2,000 yards; the maximum range was 7,440 yards.
From the 1966 manual, OP 1743, of the Mark 2 Mod 0:
Post-Vietnam, the Navy’s nascent riverine and littoral capability transitioned to Boat Support Units which later changed their name to become Coastal River Squadrons, then later the Special Boat Squadrons and SBTs, with some Mark 2s remaining in service, especially in reserve outfits, into the mid-1980s.
Likewise, the USCG kept their Mark 2s on stateside cutters– both on small 82- and 95-footers as well as high endurance 255-to-378-foot cutters– into the early 1980s.
USCGC Cape Jellison (WPB-95317) getting some time in off Seward Alaska in the early 1980s with their 81/.50 cal mount