[1] After graduating as a midshipman in 1914, he became a floatplane pilot at the start of World War I (serving with the seaplane tender Europa) and was promoted to Sub-Lieutenant in 1916.

[1][2] Later in the war he joined the armoured cruiser San Giorgio, where he was promoted to lieutenant and became navigation officer and aide of the Italian naval commander in Albania.

[1] After the fall of Rhodes, he assumed command of all Italian naval forces in the Dodecanese;[2][3] on 13 September, the Germans offered Mascherpa to surrender with "honourable conditions", but he refused.

At Mascherpa's disposal were also the destroyer Euro, two motor torpedo boats, six MAS, two minelayers and several auxiliary minesweepers and other smaller vessels; the only aircraft available were seven CANT Z.

Soon after the armistice, Mascherpa re-organized the anti-aircraft defense and persuaded the British commands to allow his ships to stay in Leros (instead of having to reach Malta like the rest of the Italian fleet), since they would be of more use there, in case of likely German attack.

[3] Frictions between the two commanders soon began, when Brittorous published proclamations where the British forces were referred to as "occupiers"; Mascherpa's protests led to change in the text of the proclamations, and he was confirmed in command of all Italian forces in Leros as well as of the civilian population, but subordinated to Brittorous.

[3] Mascherpa was not forewarned of the substitution; he was asked to go to Cairo to discuss the situation of the island, but he refused, fearing that he would not be allowed to go back to Leros to lead the defense.

[3] The British even asked for Mascherpa to be substituted, and Supermarina decided to replace him with Captain Dairetti, but this was never carried out due to subsequent events.

[3] That night, Mascherpa proposed a counterattack and Tilney approved, but the British troops assigned to this task were exhausted after a day of fighting, and were thus unable to carry out the order.

On 13 November, HMS Dulverton was sunk by Luftwaffe while trying to resupply the garrison, and a new launch of German paratroopers, though meeting stiff resistance and suffering heavy losses, was able to capture some more Italian batteries.

[5][6] On 22 May 1944 Mascherpa was tried by a Fascist kangaroo court ("Tribunale Speciale per la Difesa dello Stato"), along with admiral Inigo Campioni (the governor of the Dodecanese), on charges of "treason" for having resisted the German invasion.