One of Britain's most experienced mine warfare experts flew 6,000 miles to learn from the Japanese at their massive annual work-out.
Lieutenant Commander Jason White, who heads the elite Fleet Diving Group - responsible for specialist divers who protect British ships and ports around the world from mines and underwater devices - flew to the south-west tip of Japan to join the Maritime Self Defence Force on its mine warfare exercise.
Despite the distance separating the two nations, the two navies work together on mine warfare in the Gulf on a fairly regular basis, with Japanese dive teams using British minehunting 'mother ship' RFA Cardigan Bay as their base.
With the upper echelons of the RN keen to foster closer ties with the Japanese - the two navies, plus the US Fleet signed an agreement to that end in late 2016 - Lt Cdr White headed east to see what he could learn from the host's large-scale exercise.
They committed 21 ships and four aircraft, using some technology the RN either no longer or never has: minelayers, minesweepers and aerial mine disposal teams.
The minesweepers got down to their mission: cutting mines free from the seabed as they steamed up and down their tracks.
That left mines drifting in the ocean, so divers fast-roped out of helicopters into the water to neutralise the floating bombs - a rarely-practised art.
Meanwhile, JS Uraga was laying a fresh minefield. It's Japanese doctrine to carry out defensive mining in their own waters, so the precision with which they lay the mines is vital. She dropped 18 mines in just 30 minutes as she moved around the exercise area at 18kts.
"The speed and accuracy was impressive and something the whole crew took pride in - they even switched over the TV from the evening movie to watch the mines slide from their rails," said Lt Cdr White.
He then jumped ship to join the new minesweeper JS Hirashima and watched the Japanese performing the British observer's favourite task: hunting mines.
"Some things took more getting used to than others. Most meals consisted of miso soup, white rice and some meat or fish with pickled vegetables," he said.
"One key tip passed between divers was the pleasure of milk in tea and dunking biscuits, something the Japanese seemed to take to with some relish."
As for the war-fighting side of the exercise, Lt Cdr White returned to the RN divers' base at Horsea Island impressed by Japan's sailors, their ability and their equipment.
