The war plane struggled to gain height as one of its engines failed and only just cleared the dunes of Cable Beach before plummeting into the sea one kilometre from land and exploding on impact.

Killed were the pilot Flight Sergeant Ron Kerrigan and his navigator and best mate Sergeant Ron Smith.

Both were 20 years old.

The whereabouts of the plane was unknown until Broome historical society vice president Dion Marinis and helicopter pilot Jim Miles found the wreckage earlier this year after a two-year search.

A memorial service and unveiling of a plaque was held at Cable Beach at dawn on Thursday to mark the 70th anniversary of the crash.

RAAF Base Wagga was represented at the service by Wing Commander Jo Elkington, the commanding officer of No 31 Squadron.

The squadron was formed in Wagga on August 14, 1942, before being moved to Coomalie Creek near Darwin for war operations.

Wing Commander Elkington said the Beaufighters would fly from Coomalie Creek to Broome and then refuel so they could fly for hours over the Indian Ocean.

The squadron was disbanded in 1946 but was reformed in 2010 as No 31 (City of Wagga) Squadron and now provides airbase support services for RAAF Base Wagga.

"September of 1944 was a tragic month for the squadron," Wing Commander Elkington said.

"It lost four aircraft and seven flight crew - there was only one survivor."

Wing Commander Elkington said the service was moving and included those paying tribute to Ron Kerrigan and Ron Smith going out on a boat to the spot where the Beaufighter crashed.

Flower petals were thrown into the sea from the boat and floated over the wreckage under the gaze of Ron Kerrigan's younger sister Vall Bullied (now 85) and Ron Smith's sister-in-law Judy Smith.

About 20 of the airmen's relatives were able to attend the service.

Wreckage located includes two engines, the tyre of the tail wheel, a window frame and the tail.