Mystery solved. A friend pointed me to The Seafire – The Spitfire that went to Sea by David Brown, and it’s all described there. Indeed, pecking of the propellers on Seafires was the single most common cause of aircraft unserviceability under large operations. It was particularly so at Salerno, where, as is known, 40% of the 120-or-so participating Seafires were damaged in deck accidents only during the first day of the landings.

HMS Hunter initiated the surgeries during that operation by sawing off 2in off the blade tips on their Seafires. The trick worked: the serviceability rate at the Hunter improved and the pilots didn’t report any serious effect on performance.

Later on, it was apparently made standard practice to crop the propeller blades as much as 6in (!) from their original length. While most carriers used templates to crop the blades evenly, HMS Implacable’s repair crew used to trim only the damaged blade, up to the limit of its yellow tip. A hacksaw and a file was used. After the surgery, the pilot flying the machine run an engine check revving up to full power to see if the vibration resulting from propeller imbalance was acceptable. If it was not, another blade was cropped and so on, until the pilot thought that he could fly the aircraft.

I thought that this will be of interest to some.