Martin PBM Mariner (San Diego, 100+ fsw)

Background

I had first heard about a PBM Mariner wing section from Steve Lawson last year. Since then, Tyler Stalter and I had spent quite a few days and dives trying to find the elusive wing and ended up empty handed on all of those dives. Tyler had been at it a lot longer trying to find that damn wing.

Steve Lawson and Chris Gilmartin were the first people to find, dive, and identify the wreck (as far as we know). Below is a paraphrase of their adventure finding the wing a number of years ago:

We metered over it and then dropped in a remote operated vehicle (ROV). We immediately saw wreckage and couldn’t retrieve the ROV fast enough. At first, I thought was a B-29, given its huge size and large four bladed engines.

Email with Steve Lawson

I can only imagine the chaos and excitement they had as they brought the ROV back in and dropped in on their newly found target.

Taking pity on us, he finally relented and gave us the coordinates for the wreck which I deeply appreciate given the amount of money spent on private charters on the Marissa to find everything BUT the PBM Mariner!

PBM Mariner

The PBM is a twin-engined patrol bomber flying boat that was designed by the Glenn L. Martin company in the late 1930s and entered service beginning in 1940 and stayed in service through the 1950s. The PBM has a rich history with both the Navy and the Coast Guard. The “PBM” stands for Patrol Bomber Martin.

The PBM was used in a variety of different missions in the Navy including ant-submarine patrols and were responsible for sinking a total of 10 U-boats during WW II. The aircraft had multiple gun positions and also had bomb bays. The original version of the PBM did not have a landing gear and was strictly a seaplane (see photo below).

Photo by the U.S. Navy Museum of Naval Aviation

The PBM-5A version introduced amphibious capability by adding landing gears to the plane and became the largest amphibian ever built. Below are some photos of the -5A version showing the landing gears. The wreck that we dove was a -5A (more on that later).

The PBM is a somewhat ungainly and ugly aircraft in my opinion but it was a flying boat so that isn’t so surprising. The aircraft has a gull wing design (as can be seen in the first photo) and has a rather large wingspan of 118 feet. The wings had retractable wing landing floats.

By Bureau of Aeronautics, U.S. Navy – U.S. Navy Naval Historical Center [1], Public Domain, https://commons.wikimedia.org/w/index.php?curid=3452311

I found the image below which clearly shows the “gull wing” design that was an important factor in identifying the airplane when Lawson first found it.

Last surviving PBM at the Pima Air and Space Museum in Tucson, AZ (photo by Karsten Palt)

The PBM Wreck

Again, quoting from an email with Steve Lawson, he has a very apt description of the wreck site and how they identified it as a PBM:

The plane is upside down with parts, cables, wires and other debris left behind where the fuselage used to be (the fuselage is totally gone). What remains of the tail rests in situ with the wing, as well as part of a turret between the wing and tail.

Shortly after finding it, I contacted Pat Macha about the plane and we narrowed down the candidates based on the engines and blades. When he mentioned the gull wing of the PBM, that was the unique identifier that matched and positively ID’d the wreck.

Email with Steve Lawson

The wing is, simply put, massive. The engines are both at the site with one of them connected to the props. The second engine is next to the prop which is in the sand. It is a very photogenic wreck. Unfortunately, on the day we dove the site, the visibility was poor (15-20 feet) with a TON of particulate matter in the water so getting good photos was next to impossibly and I had to do quite a bit of work in Lightroom.

Identification

The hardest task when locating a new wreck is to identify it. It generally involves finding the type of aircraft first and then searching newspapers, military accident reports, war diaries, and other information. Fortunately, Lawson had done all that work.

In addition to being used in the Navy, the PBM Mariner was also widely used by the US Coast Guard primarily for long range search and rescue operations and there was Coast Guard Air Station in San Diego. The USCG got quite a few of their Mariners from the Navy.

Anytime you mention the Mariner and the US Coast Guard, you will likely find the name Captain Donald B. MacDiarmid or “Mac Dee” closely associated with it. Mac Dee was a character larger than life. An excerpt from the bio mentioned in the references sums it up:

“Cap’m Mac was cool and unflappable”. According to a onetime co-pilot, “Once, when we were tearing down the runway at Lindbergh Field (San Diego) in a PBY-5A, [amphibian] he dropped his cigar. He let go of the controls and started looking for the cigar under the seat. I completed the takeoff and had the gear up before he assumed command, with the cigar in its proper location.”

US Coast Guard Bio on Donald MacDiarmid by Barrett T. Beard

After the war ended, the Coast Guard became responsible for oceanic search and rescue; however, they didn’t really have any aircraft capable of doing that. The Navy gave MacDiarmid a modified PBM which was instrumented to measure structural loads for his off-shore landing tests. Previously, the Mariner really wasn’t designed to land in open ocean and instead landed in protected harbors. He tested the Mariner for three years and also experimented with using jet-assisted takeoffs (JATOs) to reduce the take-off run.

November 18, 1949

MacDiarmid was teaching new pilots his techniques for offshore landings in the Pt Loma area. During a practice landing, the aircraft hit the water and skipped back into the air, lost airspeed and the right wing stalled. The plane hit the water hard on its nose and right wing tip which resulted in the wing tip float ripping off the wing. According to bio,

The airplane plowed on ahead uncontrollable still at high speed with MacDiarmid hanging onto his arrest yelling, “Whoa, Whoa, Goddamit whoa.”

The left wing then dropped and the float on that wing was ripped off. The plane sank and the crew escaped. Below are a number of newspaper articles about the crash (thanks again to Steve Lawson for some of the clippings).

There are still some mysteries that about the actual wreck identification.

For example, what happened to the fuselage? There is a gun turret at the site and what appears to be a section of the tail, but the main fuselage is nowhere to be found. Also, it was a modified Mariner that had a landing gear but there is no evidence of that at the site.

Steve’s theory is that the plane hit the bottom upside down and the wing got “cemented” to the bottom with sand accumulation. At some point, a fishing net got caught and ripped off the fuselage and engines leaving behind the turret and wing. This would make sense since the engines would normally still be connected to the wings even after the crash.

There is another PBM Mariner crash that happened in November 1951 somewhere in the Pt Loma area as well but the newspaper articles around that time have some inconsistencies in terms of the location.

Photos

As mentioned above, the visibility was poor during our dive and there was a lot of particulate matter in the water which made taking photos without a lot of backscatter very challenging. Below are some key parts of the wreck. We are planning to make a return trip to complete photos required for a photogrammetry model.

Starboard Side Engine, Engine Mount & Propeller

On this side of the wing, the engine and propeller assembly are still connected and a short distance away from the wing. You can see the engine mount in the wing in the photos below along with one of the props that is bent.

Port Side Engine & Propeller

On the other engine, the propeller has been disconnected from the main engine.

Turret

The turret from the fuselage is out in the sand between the wing and the tail section.

Wing Sections

You can clearly see the “gull wing” design in one of the pictures below along with the leading and trailing edges of the wing in the other photos. Remember that the wing is upside down.

Tail Section

There is a section of the tail along with part of one of the vertical tail rudders close to the main wing.

Next Steps

I have been working on building a photogrammetry model of the wreck site. I didn’t quite get all sections so I have the wreck site in about 3-4 segments right now. I will post another post with the current photogrammetry model and then hopefully return relatively soon to get the missing sections to build a complete model. Below is a “teaser” screenshot of a section the model:

Wing section with the engine at the end of the wing

As mentioned, the visibility can be hit-and-miss, especially in this area. Steve Lawson was kind enough to send a couple photos they took when they first found the wreck. I’m hoping to get back to the site one day when we have similar vis:

References

Wikipedia

US Coast Guard Aviation History – Captain Donald B. MacDiarmid bio

Many private emails with Tyler Stalter & Steve Lawson

Historic Aircraft Wrecks of San Diego County by G. Pat Macha

Pima Air & Space Museum

Special Thanks

BIG thanks to Steve Lawson for providing the coordinates for the wreck along with all the research and background. Tyler and I had been looking for and wanting to dive this wreck for quite some time.

As usual, Lora and Chris on the Marissa were great along with our furry friends, Captain & Scout. šŸ™‚

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