Fisher, expanding on material in Magic–Top Secret, portrays Maskelyne as the Farnham camouflage genius whose creations baffle Army Chief, Lord Gort. Maskelyne miraculously hides a machine-gun post; he then conjures up a German battleship on the Thames.
These impressive open-air illusions are uncritically regurgitated by later commentators.
Alas, there is not a shred of evidence that these stunning tricks ever took place.
The battleship illusion is complete fiction.
In his memoirs, Indigo Days, Julian Trevelyan paints a more mundane picture of Maskelyne’s abilities: “The course included others who had espoused camouflage for one reason or another. Jasper Maskelyne’s connection with it was obvious, since disappearing was his profession and he was called in when anyone wished anything to become invisible. He entertained us with his tricks in the evenings, and tried, rather unsuccessfully, to apply his techniques to the disguise of the concrete pill-boxes that were then appearing everywhere overnight. He was at once innocent and urbane, and he ended up as an Entertainments officer in the Middle East.”
Trevelyan’s account of the Farnham course is more detailed than Maskelyne’s: “We learnt the camouflage techniques of the 1914 war, where plaster trees were erected in the night to hide snipers, and where dummy plaster heads were popped up above the trenches to draw enemy fire and to pin-point the enemy snipers’ nests.”

Rare photos of dummy heads and artificial trees can be found in the PHOTOS section of this website, under the listing 'Early Camouflage Schemes from WW1'.