In the early seventeenth century large numbers of Scots took service in foreign armies involved in the Thirty Years' War. As armed conflict between the Covenanter regime in Scotland and Charles I in the Bishops' Wars became likely, many mercenaries returned home, including experienced leaders like Alexander and David Leslie and these veterans played an important role in training recruits. Covenanter armies intervened in the Civil Wars in England and Ireland. Scottish infantry were generally armed with a combination of pike and shot, but individuals may have had weapons including bows and polearms. Most cavalry were probably equipped with pistols and swords, but may have included lancers. Royalist armies, like those led by James Graham, Marquis of Montrose (1643–44) and in Glencairn's rising (1653–54), were mainly composed of conventionally armed infantry with pike and shot. Montrose's forces were short of heavy artillery suitable for siege warfare and had only a small force of cavalry. During the Bishops' Wars, Scottish privateers took English prizes. After the Covenanters allied with the English Parliament they established two patrol squadrons for the Atlantic and North Sea coasts, known collectively as the "Scotch Guard". The Scottish navy was unable to withstand the English fleet that accompanied the army led by Cromwell that conquered Scotland in 1649–51 and Scottish ships and crews were split up among the Commonwealth fleet. During the English occupation, more fortresses in the style of the trace italienne were built.