Cold War

Martin JRM Mars – The World’s Best Firefighter

It was August 1938 when the US Navy first commissioned Glenn L. Martin Aircraft Company to build for them a brand new flying boat that could act as a slow-moving patrol bomber. The Martin JRM Mars.

The JRM Mars was the largest military flying boat ever produced and served the US military, but it spent the majority of its life in the Canadian fire services battling blazes across the forests of British Columbia.

Here is the story of perhaps the most versatile flying boat to ever operate.

The Caroline.
The Caroline JRM Mars was converted to civilian airtanker configuration in 1961.


Development and Testing

The JRM Mars was heavily inspired by the PBM Mariner, released in 1939, and was viewed as its evolutionary successor by the team at Glenn L. Martin. In November 1941 the first edition of the JRM Mars, the BuNo1520 prototype, was completed at the Martins factory located at Dark Head Creek in Baltimore.

This rudimentary version was a little different from the final product in that it possessed twin vertical tails that would later be removed.

Read More: SR.45 Princess – The Largest Metal Flying Boat Ever Built

On December 5th, 1941 during taxi testing, the prototype suffered a major outage when one of the propellers malfunctioned, tearing through the fuselage and setting engine number three alight.

Several accidents occured over its life.
The Mars was no stranger to accidents. This Marshall Mars can be seen here burning.

Repairs would be delayed and further analysis would be put on hold when two days later the USA entered World War Two after the Japanese attack on Pearl Harbour.

It would take until July 2nd, 1942 for the long-awaited maiden voyage of the JRM. As the war raged on, however, advances in military technology developed at such an astonishing rate that by the time the JRM Mars was ready, slow-moving bombers were a thing of the past, having been replaced by other warplanes boasting greater speed and range.

Consequently, instead of being a craft designed to unleash explosive projectiles on the Axis powers, it was decided that it could be more usefully employed as a military transport.

The Mars was at home on the water.
The Mars was happiest in the air or on the water.

As a result, the JRM Mars, given the new moniker XPB2M-1R, was overhauled, and its gun turrets, wing bomb bays, and armoured plating were swapped for the extensive cargo hatchings and cargo loading equipment it would need to fulfill its new obligations.

US Navy Service

Freshly renovated, the XPB2M-1R JRM officially entered the service of the US Navy in November 1943, being operated by members of the newly-formed VR-8 unit before being re-assigned to the VR-2 unit based in San Francisco.

It was here that this first model, affectionately nicknamed Old Lady, performed admirably transferring soldiers between California and Hawaii, convincing Navy officers impressed by its safety record to order a further 20 models, although this was eventually reduced to 6 by the end of the war.

It looks great in Navy colours.
The Mars that are still flying today do not wear the Navy colours. Photo credit – Bill Larkins CC BY-SA 2.0.

When the first shipment of JRMs was dispatched in July 1945, they arrived having undergone some considerable tweaks.

Now possessing a single vertical tail, a longer hull with fewer bulkheads, a larger maximum take-off weight, and a newly installed array of Wright R‑3350‑24WA Cyclone engines driving four blades, they differed from their predecessor considerably.

The aircraft produced were named after islands in the Pacific and were called the Mariana Mars, Philippine Mars, Marshall Mars, Caroline Mars, and the Hawaii Mars II, which replaced the original Mark I version following an accident in 1942.

Four engines of the Philippine Mars
The Philippine JRM Mars’ engines. Photo credit – Kevstan CC BY-SA 3.0.

A couple of the newly delivered flying boats were JRM2s, which had been constructed with superior Pratt & Whitney R‑4360 Wasp Major engines, making it possible to carry even heavier loads on the California-Hawaii route.

Read More: VZ-9AV Avrocar – Mach 4 Flying Saucer

It persuaded policymakers to later swap the Wright engines of the four JRM1s to the Wasp, turning them into JRM3s additionally equipped with reversible-pitch units for greater control.

The JRM2 and JRM3s faithfully served the US military until their last flight in August 1956, before all 6 were withdrawn from service and beached at NAS Alameda. During its stint with the US Navy, the Carolina Mars set the passenger-hauling world record in March 1949, shipping 269 people from San Diego to Alameda.

Four Navy JRM Mars flying in formation.
The Mars was used by the navy initially and could carry large numbers of troops.

But there were also some low points, with one Marshall Mars crashing off the coast of Honolulu in April 1950.   


During the mid to late 1950s, western Canada was struggling to put out the forest fires ravaging its provinces.

These natural disasters were seriously affecting the profit margins of several major lumber corporations including MacMillan-Bloedel, the TimberWest Forest Corporation, and Pacific Forest Product, who formed the Forest Industries Flying Tankers (FIFT) to address the issue.

Recognizing that there were very few airfields but an enormous amount of lakes in the affected region, Dan McIvor, chief pilot at Macmillian-Bloedel, suggested that a flying boat with fire-fighting capabilities might be the solution to their woes.

A water bombing demonstration at the 2010 olympics
Several JRM Mars was converted into water bombers to help put out fires. Photo credit – Province of British Columbia CC BY-SA 2.0.

Following their auction to the Mars Metal Company for a miniscule 23,650 dollars, 4 of the JRM Mars flying boats were saved from the scrap heap by McIvor, who bought each one for 25,000 dollars each in 1959.

They were then transported to their new home on the western coast of Canada to Port Alberni/Sproat Lake Tanker Base on Vancouver Island.

In a move that enabled the JRM Mars to operate well into the 21st century, McIvor intuitively bought a wealth of replacement parts relatively cheaply, paying just 135 dollars each for 6 spare engines and 3200 dollars for numerous crates crammed full of factory-new components.

A pair of Mars sat in dry dock for service.
A pair of Mars sat in dry dock. Photo credit – RuthAS CC BY-SA 3.0.

He was even able to get his hands on a complete JRM nose, which came from the aborted 7th JRM 3 abandoned after the US reduced the order size.

The JRMs were completely refurbished in the early 1960s at Victoria Airport by Fairey Aviation, engineers removing all of the unnecessary features originally installed to maximize its effectiveness as a military transport.

As well as updating the Cyclone engines, the JRMS were furnished with voluminous water tanks supplied by a retractable scoop system that would transform it into an efficient aerial fire-fighter.

The JRM Mars prototype.
The prototype Mars had much less powerful engines than after the upgrades.

The program suffered an early spell of misfortune, with the Mariana Mars being destroyed and killing all 4 of her crew while fending off a fire in June 1961, and the Carolina Mars being lost to Typhoon Freda in October 1962.

Thankfully, the Hawaii Mars and the Philippine Mars never had a major accident, enjoying a career that would last over 50 years.

JRM Mars

The Martin JRM Mars was 35.74 metres long, 15 metres high, and had an empty weight of 34,279 kilograms. It had an enormous wingspan of 61 metres, even bigger than that of a Boeing 747-300, and a wing area of 342 metres squared.

The JRM Mars is huge.
The size of Mars can be appreciated from the air. Photo credit – Michael Maclean CC BY-SA 3.0.

It was fitted with four 18-cylinder, 2,200‑hp Wright R‑3350 Duplex-Cyclone engines which gave it a top speed of 221 mph, a cruising speed of 190 mph, and a range of 4948 miles as well as a maximum altitude of 14,600 feet.

Like other conventional flying boats it had a large rounded hull and its flight deck was highly mounted, offering excellent visibility. Its wings were straight with curved tips and were each installed with a two-strutted pontoon to prevent it from tipping into the water.

Read More: Bristol Beaufighter – Night Stalker

In its role as a military transport, it could carry up to 133 soldiers or 7 light combat vehicles and had the capability of evacuating 84 injured men and 25 medical staff.

The Hawaii Mars also crashed.
The Marshall Mars was not the only one to be damaged. Hawaii Mars also crashed in Chesapeake Bay in 1945.

In its fire-fighting capacity, it could carry up to 27,276 litres of water which could be turned into foam by combining it with a chemical concentrate that resided in a separate tank.

The two surviving craft that held this function had a few notable differences, with the Philippine Mars dropping its load from two inlets on either side of the fuselage and the Hawaii Mars jettisoning its water reserves from its belly.

The Philippine Mars had a large fuel capacity at 49,692 litres, in comparison to Hawaii’s 24,550 litres, because the water tanks of the latter were located where its old fuel containers had been situated originally.

The JRM Philippne Mars.
The JRM Philippine Mars had bigger water tanks than the Hawaii. Photo credit – Alex Juorio CC BY-SA 2.0.

Both fire-extinguishing air vehicles were manned by a crew of 4 comprising of a pilot, a first officer, and two flight engineers. To refill the water tanks, the plane landed on the water and was set to a speed of 80 miles per hour.

Next, one of the engineers would activate the water scoops, two forward-facing pipes with an 18-centimetre diameter, and it would take 25 seconds at a rate of 1000 litres per second to fill up to capacity.

The other engineer would ensure that as the plane got heavier with the intake of water that the craft maintained a speed of 75 mph by ramping up the power of the engines gradually.

Philippne Mars at Sproat Lake.
The Philippine Mars sat at Sproat Lake. Photo credit – Ken Fielding CC BY-SA 3.0.

The modified JRMs couldn’t be matched, on average being able to drop a load of water every 15 minutes and up to 20 times before the foam concentrate ran out.


The Hawaii Mars and Philippine Mars worked so well that they continued to be called upon even after the turn of the millennium, but the development of cheaper alternatives and the decreasing reliability of the aged flying boats would soon seal their fate.

In November 2006, they were sold to the Coulson Group also based in Vancouver, who made ambitious plans to upgrade the avionics and communications systems.

However, their program was obstructed by the provincial government of British Columbia, which pointed to the existence of modern options that were less pricey and more efficient.

The Philippine Mars in Navy service.
The Philippine Mars in Navy service.

They were also reluctant to continue funding an aircraft that was nearly 50 years old, struggled in mountainous terrain, and only had at its disposal 113 bodies of water large enough for it to refill its water supply.

Read More: Tupolev Tu-128 Fiddler – The Bomber Sized Fighter

The Philippine Mars would extinguish its last fire in the summer of 2006 before settling into its new home at the US Naval Aviation Museum in Florida.

 The Hawaii Mars continued to work for the authorities of British Columbia until its retirement was announced in May 2013. It made a brief comeback in July 2015 following a particularly bad bout of forest fires that summer.

Thanks to high public demand, it was awarded a one-month contract that cost 15,000 dollars a day and 11,000 dollars per flying hour.

The moderinised cockpit of the JRM Mars
The cockpit of the remaining Mars have been modernised. Photo credit – Kevstan CC BY-SA 3.0.

Its final flight occurred in July 2016 at the EAA AirVenture Oshkosh Air Show before it was stored at Sprout Lake. As of 2022, Hawaii Mars is currently looking for a new owner, having been put up for auction by Platinum Fighter Sales. Simon Brown, overseeing the deal, has commented:

 “It would be the crown jewel of any collection—but the buyer would need to have a big lake.”

After 77 years, Hawaii Mars remains the last flight-worthy Martin JRM Mars in existence. Hopefully, its next keeper, whoever that may be, can treat this piece of aeronautical history with the reverence and respect it deserves.

If you like this article, then please follow us on Facebook and Instagram


  • Crew: four (with accommodations for a second relief crew)
  • Capacity: JRM Mars – 133 troops, or 84 litter patients and 25 attendants or 32,000 lb (15,000 kg) payload
  • Length: 117 ft 3 in (35.74 m)
  • Wingspan: 200 ft 0 in (60.96 m)
  • Width: 13 ft 6 in (4.11 m) Hull beam
  • Height: 38 ft 5 in (11.71 m) afloat, 48 ft (15 m) beached
  • Empty weight: 75,573 lb (34,279 kg)
  • Max takeoff weight: 165,000 lb (74,843 kg)
  • Powerplant: 4 × Wright R-3359 Duplex-Cyclone 18-cylinder radial engines, 2,500 hp (1,900 kW) each
  • Maximum speed: 221 mph (356 km/h, 192 kn)
  • Range: 4,900 mi (8,000 km, 4,300 nmi)
  • Service ceiling: 14,600 ft (4,500 m)
  • Full water tank load: 7,200 US gal (27,000 l; 6,000 imp gal)