X MAS

Decima Flottiglia MAS
Decima Flottiglia MAS arm badge during the  Italian Social Republic (Nazi occupation of Italy).
Active	March 1941–September, 1943
Country	Italy
Branch	Regia Marina
Type	Naval commandos
Role	Frogmen, manned torpedoes,
Nickname(s)	Xª MAS
Motto(s)	Per il Re e la Bandiera. (For the King and for the Flag)
Equipment	SLC "Maiale" torpedoes MTM "Barchini" motor assault boats
Engagements	Souda Bay, Gibraltar, Alexandria, Algiers, sank HMS Queen Elizabeth, HMS Valiant, HMS York, HMS Eridge and 20 merchant ships
Decorations	Golden Medal of Military Valour Individual decorations: 29 Golden Medals of Military Valor 104 Silver Medals of Military Valor 33 Bronze Medals of Military Valor
Commanders
Notable commanders	Vittorio Moccagatta Ernesto Forza Junio Valerio Borghese

Mariassalto
Active	October 1943–April 26, 1945
Country	Kingdom of Italy
Branch	Italian Co-Belligerent Navy
Type	Naval commandos
Role	Frogmen, manned torpedoes
Equipment	Chariot
Engagements	Raid on Genoa Raid on La Spezia
Commanders
Notable commanders	Ernesto Forza

Decima Flottiglia MAS
Decima Flottiglia MAS arm badge during the  Italian Social Republic (Nazi occupation of Italy).
Active	September 1943–April 26, 1945
Country	Italian Social Republic
Branch	Navy
Type	Naval commandos
Role	anti-partisan
Nickname(s)	Xª MAS
Motto(s)	Memento Audere Semper (Remember to dare always)
Commanders
Notable commanders	Junio Valerio Borghese

Per il Re e la Bandiera. (For the King and for the Flag)

The Decima Flottiglia MAS (Decima Flottiglia Mezzi d'Assalto, also known as La Decima or Xª MAS) (Italian for "10th Assault Vehicle Flotilla") was an Italian commando frogman unit of the Regia Marina (Italian Royal Navy) created during the Fascist regime.

The acronym MAS also refers to various light torpedo boats used by the Regia Marina during World War I and World War II.

Decima MAS was active during the Battle of the Mediterranean and took part in a number of daring raids on Allied shipping. These operations involved surface speedboats (such as the Sinking of HMS York), manned torpedoes (the Raid on Alexandria) and Gamma Frogmen (against Gibraltar). During the campaign Decima MAS took part in more than a dozen operations which sank or damaged five warships (totalling 72,000 Gross Register Tonnage) and 20 merchant ships (totalling 130,000 GRT).

In 1943, after the Italian dictator Benito Mussolini was ousted, Italy left the Tripartite Pact and joined the Allies. Some of the Xª MAS men who were stationed in German-occupied northern Italy enlisted to fight for Mussolini's newly formed Italian Social Republic (Repubblica Sociale Italiana or RSI) and retained the unit title, but were primarily employed as an anti-partisan force operating on land. Other Xª MAS men in southern Italy or other Allied-occupied areas joined the Italian Co-Belligerent Navy as part of the Mariassalto (Naval Assault) unit.