Amateur wreck hunters are believed to have solved a 70-year-old mystery, locating the final resting place of two men killed in a plane crash during World War II.

The RAAF Beaufighter pitched into the sea off Broome on a dark night in September 1944, killing the pilot and navigator onboard.

Searches conducted in the days after the crash found no sign of it, and Sergeants Ronald Kerrigan and Ronald Smith were listed as missing in action.

Ronald G Smith (L) and Ronald Stephen Kerrigan (R) were onboard the RAAF Beaufighter when it crashed. ( Supplied: Val Bullied )

Two years ago, experienced wreck hunter Jim Miles teamed up with Broome historian Dion Marinis to try to locate the site.

After scouring the ocean floor for months, they have located what they believe to be the plane debris, laying less than two kilometres off Broome's Cable Beach.

"A lot of people had forgotten about it," Mr Marinis said.

"I did some research and talked to old hard hat divers, and they did remember vaguely.

"We've been doing a lot of side-scan imaging of the ocean bed to try to find this wreck, so that takes a lot of time.

"Because it's in a rock field, this aircraft, it's been very difficult to find and obviously with the Broome weather - there's only a small window at times that you can do that."

While the site is yet to be formally assessed for heritage listing, both the RAAF and the WA Museum have agreed the wreck appears to be appears to be the long-lost plane, and offered the searchers their congratulations.

The sergeants were based in Darwin and were part of 31 Squadron, which was comprised of heavy strike fighters.

The pair was doing an exercise out of Broome, shadowing Catalinas which were laying mines out in the shipping channel to stop the Japanese boats.

Commitment made to find the wreckage

Divers check out the tail of the RAAF Beaufighter, A19-163 crash site, off Broome's Cable Beach, June 2014 ( Jim Miles )

Mr Maranis says the sergeants were really good mates and had flown together on a large amount of missions.

His search partner Jim Miles believes the flight crashed not long after take-off.

"What we believe is that the aircraft experienced an engine failure on take-off at night, on a very dark night in 1944," he said.

"It took off straight towards sea from the main runway at Broome, which is the same runway we have today.

"The pilot was unable to control the aircraft in the pitch-dark with limited instrumentation and I believe he ploughed into the ocean with a very steep angle of descent."

Mr Miles said the aircraft more than likely fell into many pieces with the high impact of the crash and killed both men onboard instantly.

"For me, when you find a wreck that no-one else has seen, and you've expended so much energy, it really is a spiritual moment," he said.

"The moment when you come across a wreck like this, it really is a spiritual moment because you're so intimate with the history of what's happened, it's quite an overwhelming experience."

The RAAF Beaufighter A19-163, which is believed to have crashed off Broome during WWII. ( Supplied: Val Bullied )

Mr Maranis said he made a commitment to relatives to see if they could find the wreck.

"Jim found a window frame off the Beaufighter which we've been able to match to the one in the museum in Moorabbin," he said.

"I did a dive with my son, he was out with me on the boat, so I dived down to the tyre of the tail-wheel, it was quite a large substantial debris field.

"Then we came out and dived it. That's when I came across and found the engine, and that was quite an amazing moment to find something quite substantial.

"I feel quite emotional at times about it because I do realise there are two lost men whose bodies were never recovered," Mr Marinis said.

"So I think it should be protected and I guess people should be aware that men were called off the coast of Broome, trying to defend the country."

Pilot Ronald Kerrigan's sister Val Bullied was 15 years old when her brother was killed.

The 85-year-old still lives in Perth and says news of the discovery came as a shock.

"I'm very appreciative of Dion and his friend Jim who've done all the work," she said.

"I'm very pleased actually, I never thought it would happen, not after all that time, I mean it's 70 years in September, it's a long time."

An application will be made to have the site added to the state register of heritage places.