They towed the Horsa Glider DP329 when one of the engines caught fire near the Portuguese coast, and they had to ditch.

The aircraft fuselage broke and one sunk very fast taking with it the navigator, Sgt. Cox. The rest of the crew was able to get into the dinghies and joined the three crew members from the glider that had made a perfect landing.

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Williamson's logbook and the telegrams received by the family after he crashed at sea and after he arrived back in England.
(Jonathan Williamson)

They were in the dinghies for nine hours before a Spanish ship picked them from the sea and landed them in Bilbao, two and a half days later.

In the city they contacted the consulate that send them to Madrid. From the Spanish Capital they were sent to Gibraltar where they arrived at August 28.

Cox is remembered in the Runnymede Memorial.