The team: Tim Welford (left) and Dom Mee

But no one should underestimate the scale of the challenge they have set themselves.

In the words of the Ocean Rowing Society: "This is the most difficult route of all because of the currents, the winds and the severe weather conditions."

Tim, 33, and Dom, 29, joined the Royal Marines on the same day in 1988.

Their careers have taken them around the world and given both of them a taste for adventure.

"I cut my teeth six years ago skiing across Iceland," said Tim.

"I rowed the Atlantic in 1997. It was an amazing experience. But the North Pacific is the holy grail of ocean rowing."

That 1997 Atlantic challenge saw Tim and his team mate Wayne Callaghan finish sixth, completing the journey in just 60 days. Eight of the 30 teams did not finish.

Dom too has had his fair share of adventure.

Challenge facts

Start: Choshi, Japan Finish: San Francisco, USA Distance: 5,000 miles Time: Target 120 days Current record: 133 days Daily rations: 6,000 calories

Trained in jungle and Arctic survival, he has also sailed at international level competitions including the Sydney to Hobart race and the Fastnet.

"It's a great adventure and I have always been a bit of an adventurer, right from when I was a little boy climbing trees," said Dom.

"But I'm also interested in what kind of person I will be at the end. I'm very keen on trying to be a better person and want to develop from within."

Despite having no previous ocean rowing experience, Tim was convinced that Dom was the right man to have on board for the Pacific challenge.

"Dom's very focused and when he has an idea between his teeth, he bites hard and does not give up until he has achieved or given it the best of his ability," said Tim.

"During the planning for the trip he has been able to deal with things like the sponsorship and publicity while I have concentrated on the technical side. It's been a great division of labour."

Mental preparation

While proper physical preparation is crucial, maintaining an even mental keel plays an important role, said Tim.

"The camaraderie among us is also very strong. Humour is very important because the best time to laugh is when you are down on your chin straps."

Here's how not to do it...

Dom added: "There's going to be times when we are down. But we are different enough people to know that when one of us is down, the other will be able to buck him up. We'll be keeping each other going."

While some people would dismiss such words as bravado, Dom says this approach is crucial for maintaining the right frame of mind.

"You have to be prepared mentally all the time," he said. "For the past two years it's been on my mind morning, noon and night. "It's going to be hard. There's going to be times when we doubt ourselves, that's normal. But we have to keep a firm focus on the goal."

Days before leaving, he predicted that the hardest part for him would be the early stages.

The rowing regime means that each man will be spending three hours at the oars and then three hours off - 24 hours a day.

Not only will the body be put under immense physical stress, normal work and sleep rhythms will also be left on the shoreline.

Tim is more relaxed about the actual effort itself. What concerns him is the weather.

"Fear is a wasted emotion but apprehension definitely comes into it when you're dealing with the weather," he said.

"You don't know what it is going to do until it hits you. The problem isn't so much rough weather because the boat can handle that.

"But when it's blowing on the nose of the boat and we're unable to row, we're just sitting there bobbing around and eating rations.

"That was the most depressing time of the Atlantic trip. We were blown back 120 miles in seven days and there was nothing we could do."

Keeping in contact

Tim and Dom are also embarking on the trip with the support of their wives and families. Making sure that they can contact them has played an important role in the planning of the bid.

Not only will they be able to e-mail home, but they have sophisticated satellite communications equipment so that they can talk to them directly.

For the past week, Crackers has been the star attraction at the British Embassy in Tokyo.

It is now bobbing in the harbour at Choshi, every last conceivable test carried out, waiting for its crew to step on board. What will their thoughts be as they row away from the shore?

"It's all going to be about being able to visualise the goal," said Dom.

"I can see myself rowing underneath the Golden Gate Bridge in San Francisco. "And I tell myself that it will happen."

You can contact Tim and Dom through BBC News Online. Click on the link on the top right for more.