PTF Firepower

Gunnery exercises aboard PTF’s.  (Bad Guys take note…) Here’s a “shot” of GMG2 “Bobby” and GMG2 (SEAL) “Bob” preparing to fire an 81 mm mortar flare round.  The Browning M2 .50 Cal has been dismounted. Bobby has pulled up on the trigger “cock” handle which retracts the mortar firing pin.  Sliding the round home, the weapon can be pointed horizontally in a “direct fire” mode and fired by pulling the trigger.  An 81 mm howitzer.  It’s called the Mk2 Mod 0 gun system.

You can see the mortar sight quadrant near the sound-powered phone mouthpiece.  Sets azimuth and elevation, which in conjunction with range tables and the number of propellant increments clipped on, determines where the round will hit.  More or less.. From a moving, rolling boat deck this is done mainly via experience and ‘Kentucky Windage”.

It can also be fired in the conventional mortar-mode by not retracting the firing pin.  It goes off once the round contacts the pin.  A very effective weapon.  A common usage would be (at night) to fire a flare round over the target’s head, well beyond him and illuminating him from behind – then you fire your main weapons at his sillouette.  It also reduces self-illumination in that manner.

The flare fuze is set by inserting it in the fuze setter installed on the port side of the ammo ready service locker.  Rotate the round so the fuze is set to the desired time delay, pull the pin and then fire it.  One favorite “ship handling” training exercise was to try to land the burned-out flare parachute on the deck by chasing it and manovering under it.  Pretty tricky.  Photo: Tim Sammons

Below is photo sequence from another day firing the 81 mm. In this case, note that the loader had dropped the round and is protecting himself from the blast.  In the second photo the round has fired and the barrel has recoiled about 6 inches backward relative to the recoil cylinder; the round is likely still inside the barrel making its way out when the photo was taken.  Note the muzzle flash hider mounted on the .50 Cal M2 barrel  Photos: Tim Sammons


Below is a view of the 40 mm gun being fired. There is a lot going on in this photo.  EM1 “Mac” (foreground) is the Trainer, slewing the mount in azimuth.  The Pointer is on the other side of the gun and he sets the elevation of the gun.  He also fires the Gun with the foot trigger.  GMG2 (SEAL) “Bob” is the Loader as he prepares to load another 4 round clip into the feeder where 8 already reside waiting to be fired.  Note that the Ensign has been tied off to prevent if from slapping the Loader in the wind.

The particular round being fired is the HE-I-T/SD (High Explosive Incendiary Tracer/Self Destruct variant.  It has a maximum range of 6 nautical miles but the maximum effective range is much shorter.  This round would self detonate at 4000-5000 yards if it didn’t hit anything first – but it still had a point-detonation fuze.  The intent in anti-aircraft service was to put out a wall of high velocity shrapnel at that range that an enemy aircraft had to fly through.  It also reduced the friendly fire potential, a serious consideration in large fleet formations under air attack.  When fired, you could see the tracer all the way out and when you hit that 55 gallon drum, a bright flash and puff of gray smoke indicated detonation.  It was also a good training round due to this “self limiting” maximum range.  The Gun fires more than 2 rounds per second and is technically a “machine cannon”, being fully automatic.   Boom boom boom boom boom boom boom boom …Serious weapon.

Often called a “Bofors” Gun it is actually a US-manufactured weapon built by Chrysler Corporation, one of about 60, 000 they made during WWII.  We redesigned it under license from Bofors (Sweden) to eliminate the numerous hand fitted, gun-specific parts that Bofors was utilizing.  “File this part to fit upon final assembly”.  This did not lend itself to mass production or field repair parts logistics, so some redesign was made.  It was also redesigned for SAE “English” tooling versus the metric dimensioning in the original Swedish design. Approximately 26 nations used this gun or close variants.  It is still in use today – including on the AC-130 Spectre Gunships.

This particular gun aboard PTF-17 was a replacement, recently arrived from the Naval Ammunition Depot, Crane Indiana.  It was still in its Haze Gray paint and was apparently someone’s Mount 212 as indicated by the stencil on the elevation spring housing.  Photo:  Tim Sammons

Fun Fact: When we received the boats at CRD21 the pointer and trainer foot rests had wooden blocks installed to better fit the shorter-statured Vietnamese allies. This included a wooden block on the trigger pedal. The bridge decking was also built up with nicely varnished wooded “hatch cover” plates to allow the RVN sailors to see over the dashboard.

FIREPOWER:  We carried approximately 20 M-16 Rifles, four .45 cal pistols, two .38 cal pistols, two M-60 machine guns, two M-79 grenade launchers, two M-870 12 gauge shotguns, a 40 mm Very pistol, a .45/70 line-throwing gun plus the .50 cal M2, two 20 mm cannons, the 40 mm cannon and the 81 mm mortar. Without a doubt, the most heavily armed vessel of its size anywhere. Here’s some more photos of a typical day at work.  Photo:  Tim sammons

The 20 mm guns were a bit of an enigma to me. When we received the boats, they had the Oerlikon 20 mm guns of WWII vintage. They were mounted on deck on either side of the bridge. This gun utilized the 60 round drum-type magazine and a reasonable photo of one is in the photo of Admiral Kauffman aboard PTF-17 on the CRD21 Ops posting. For some reason I don’t think we ever fired them, at least on PTF-17 or PTF-18 while I was aboard. It could be because we didn’t have any of the Gunners Mates with current “service record” school qualifications on them and even though the Navy’s Gunners Mate Class “A” School was at Great Lakes we may not have been qualified on them. They may have stopped teaching them at some point.

Some time during my tour we replaced the Oerlikons with the MK-16 belt-fed 20 mm guns. I remember having to modify the two armor plates from the Oerlikon mount to accommodate the MK-16’s. That required drilling new bracket holes in the plates and we must have worn out about a dozen drill bits trying to penetrate that armor plate. Tough stuff! Below is a photo of GMG2 “Jack” with the new MK-16 gun mount aboard PTF-18. Photo: Tim Sammons

While I was on active duty I don’t recall ever firing the MK-16’s either. Maybe CRD21 did after I left active duty and joined the Reserve crew in August 1975 but I don’t recall it. I have a vague memory of someone telling me that a 20 mm round detonated inside a gun, bird-caging the barrel. If that actually happened, maybe we became “gun shy” or were directed not to fire them again. Vague recollections: Any CRD21 guys recall the situation with either of these guns?

M-60 Practice.  We usually mounted the M-60’s in the searchlight pintles on either side of the bridge, over the 20 mm gun mounts. There was a cutout with a removable plywood cover in the decking for the lookouts / gunners and it was well positioned. The M-60 could be fired single-shot; it had a flat trajectory and was VERY accurate. Note the 81 mm mortar fuze setter on the ammo box (dark circle). Note the lamp assembly above the fuze opening to facilitate fuze setting in the dark. Photo:  Tim Sammons

Below: The Browning M2 .50 Cal heavy machine gun on the Mk2 Mod 0 system.  Another serious weapon.  After a healthy burst, the crew would light their cigarettes on the hot barrel.  If a round was still chambered after you had fired a burst, that round would eventually “cook off” from the heat retained in the chamber – very dangerous – keep the gun pointed down range at all times.  NEVER walk in front of it! On rare occasions, a .50 cal round would hit a wave face at such an angle that it would come straight back at us.  Weird. How could that happen? It sounded like a 10 pound bumble bee whizzing over your head.  Never got any dings in personnel or the boat but it was scary when it happened.  Note the lack of hearing protection – this was the “Old Navy”, not good…I’m paying the price for it now….
Although not evident in this faded photo, the .50 Cal ammo projectiles were color coded. We usually fired a mix including – Armor Piercing, Incendiary, Tracer. This was a repeating, 5 round sequence consisting of those 3 types plus 2 Ball rounds. Bad news for bad guys…
Photo: Tim Sammons

Don’t forget the pre-firing set up of the M2 using your handy Head Space and Timing gauge – to prevent the gun from blowing up in your face. Also, never charge the weapon by grabbing the handle with your palm facing forward – a cooked off round will drive the handle rearward, shattering your wrist. Keep that palm facing you!

Below: Loading and Firing the 40 mm with ammo made in 1944.  Photo: Tim Sammons

Fun Fact: When the projectiles you see below detonated, they sprinkled fragments of steel across the bottom of Lake Michigan. Then they rusted, becoming iron ore. During the first half of the 20th century much of the iron ore (steel) used in the US armaments buildup to fight WWII came from the Mesabi Iron Range, not far from here in Minnesota and extending out into Lake Superior and into the Upper Peninsula of Michigan and Wisconsin. The worlds largest iron deposits. The 40 mm rounds you see here were manufactured in 1944. In a real sense, that iron was “going home”.



We were AWESOME !! Another “floating Mine” destroyed.