The SAS needed a combined incendiary and explosive device light enough to be carried by a small group of commandos yet powerful enough to destroy and set fire to aircraft on an enemy airfield.
[3] Inside the mass was inserted a two-ounce (60 g) dry guncotton booster, plus a detonator attached to a thirty seconds fuse.
Alternatively, Lewes bombs could be triggered by pencil detonators or booby-trap firing devices such as pressure release switches.
A disadvantage of the Lewes bomb was that the detonators could be unreliable; several raids failed when their pencil-detonators were rendered unusable by heavy rain.
However they also noted that the fires did not "seem to have been due to any particular qualities of the explosive, but to the accurate placing of the charges in proximity to the fuel tanks" [6]