The de Havilland Aircraft Museum has set a world first by adding a rare wartime “bouncing bomb” to its historic collection of iconic, locally-built aeroplanes.

A Barnes Wallis-designed half-ton Highball - a spherical version of the Dambusters cylindrical bouncing bomb - was delivered to the museum at Salisbury Hall, London Colney, on Sunday.

It was brought from the depths of a Scottish loch by a Scuba diving team who had raised it from a depth of 35 metres just four days earlier.

St Albans & Harpenden Review:

“The Highball was designed to be dropped by de Havilland Mosquitos, and as our museum has three of these aircraft we were more than delighted to be asked if we would like to have it,” said museum curator Alistair Hodgson.

Because the bomb has been at the bottom of a seawater loch for 74 years since it was dropped by an RAF Mosquito in 1943, it must be kept in a tank filled with a special solution to reduce the corrosive effect of the salts absorbed from the sea.

“It is in remarkably good condition but it is likely to be two years before we can take it out of the tank and put it on display,” said Mr Hodgson.

The Highball is a smaller version of the bouncing bomb codenamed Upkeep, which Barnes Wallis designed for 617 Squadron to use on their air raid on three dams in the German Ruhr Valley in 1943.

Some 200 non-explosive practice Highballs were dropped by specially modified Mosquitos of 618 Squadron on Loch Striven in Argyll, which was chosen as the bombing range. The targets used were two retired battleships.

However live versions of the Highball were never used in anger.

“The story of the Highball and 618 Squadron is not generally well known and at the de Havilland Museum we will be creating a special display alongside our many other exhibits to tell visitors all about it,” said Mr Hodgson.

The second Highball will be donated to the Brooklands Museum in Surrey in October.