First Baron Montacute. One of the first admirals, served in senior positions in Norman wars in France, Wales, and Scotland.

Served in Welsh war against Llywelyn ab Gruffydd, 1277; also in successful campaign again in 1282; commanded a ship which broke French siege of Bordeaux (then English), 1296; in Gascony till 1297; battle of Falkirk, 1298; wars against Scotland, 1299; Governor of Corfe Castle, 1299; signed and sealed "the famous letter of the Barons to the Pope", 1301; siege of Carlaverock, 1300; Scottish wars till 1307; governor of Beaumaris Castle, 1308; Admiral of the Fleet (employed against the Scots), 1310.

Descendent of Drogo. Married Aufricia, daughter of Fergus, king of Man.

Denholm-Young provides some information on what it meant to be an admiral in 1307:

"A more traditional type of admiral was Lord Simon de Montague, a king's banneret and a baron, appointed in 1307 as Captain and Governor of the whole fleet. Simon, who bore golden griffins on a blue banner at Caerlaverock, was Constable of Corfe and later Beaumaris. He is said to have served in all Edward's wars.

After 1293 the war, not yet declared on land, was growing in intensity between merchant fleets at sea, and the control of this in the interests of the king and his subjects led to the appointment, for the first time, of admirals. There was as yet no Royal Navy, though the king had a ship or two... The nucleus for a war-time fleet was provided, under a standing agreement, by the Cinque Ports, and the rest were, like their crews, impressed... the crews had from time to time to be prosecuted because they "withdrew without licence", as in 1302 and 1303... The ships, merely armed merchantmen, with soldiers on board if battle was intended, sailed in convoy. As on land, the opposing sides sometimes agreed upon a time and place for battle...

...

These ad-hoc fleets helped to conquer Wales by cutting off supplies from Llewelyn. They assisted in the Scottish campaigns by transporting supplies to Scotland, and elsewhere by protecting merchant ships or even ports from attack; but most of all transporting men, horses, and bullion ... naval warfare, in the absence of guns, inevitably consisted in boarding and capturing enemy ships, with the aid of archers and "Greek fire" hurled from slings." (Denholm-Young).

Denholm-Young provides the footnote: " Simon de Montague castellated Yerdlingham, co. Somerset. He was appointed 30 January 1307 ( CPR, p. 490)."

The Cinque Ports were the English "international airports" of the times, that is, they were ports engaged in "international" trade (the concept of the nation-state did not really exist at the time). They were somewhat similar to the Hanseatic League.

Note that his family arms, a single male griffin, was supposed to be the family's original arms and was also ascribed to Osmond.

Sources:
The Dictionary of National Biography.
The Dictionary of Heraldry.
Vita Edwardi Secundi, N. Denholm-Young, trans.
History and Heraldry, N. Denholm-Young.

http://www.montaguemillennium.com/familyresearch/h_1317_simon.htm