Which book was the 1980 film, 'The Sea Wolves' based on?

'The Sea Wolves' was a 1980 war film starring Gregory Peck, Roger Moore and David Niven. The Panavision film is based on the book 'Boarding Party' by James Leasor, which itself was based on a real incident which took place in World War II.

The incident involved Operation Creek, the Calcutta Light Horse's covert attack on 9 March 1943 against a German merchant ship, which had been transmitting information to U-boats from Mormugão Harbour in neutral Portugal's territory of Goa.

During World War II, German submarines are sinking thousands of tons of British merchant shipping. British intelligence, based in India, believes that information is being passed to the U-Boats by a radio transmitter hidden on board one of three German merchant ships interned in Goa, then a colony of Portugal. Portugal was neutral during the Second World War; the ships cannot be attacked by conventional forces.

The head of the Indian section of Special Operations Executive authorises attempts to kidnap and interrogate two known German agents, but these operations both fail. An approach is then made to a territorial unit of British expatriates, the Calcutta Light Horse, to carry out the mission on its behalf. They all volunteer – all are trained in military skills and keen to 'do their bit'.

The raiding party sail around the coast in a decrepit and barely seaworthy barge; they set mines on the hull of the German ship in Goa. They catch the depleted crew off guard. The raid is a success.