It was not until the reign of Charles I that any British warships entered the Baltic, for it took a combination of a ruler keen to exercise his sea power, and possessed of suitable ships to do so, together with a major threat to the British position. Not until the reign of Charles I did this combination exist, and not until his successor was threatened did a powerful intervention happen.

The possession of a state navy had been unusual in the Middle Ages. If a ruler such as Henry V (1413–1422) planned an overseas expedition, merchant vessels were requisitioned for the transport of the forces and their supplies, and were returned to their owners afterwards, if they survived. Kings intermittently had ships built for their own use, but these were expensive to maintain and were either allowed to rot or were sold off; more often kings purchased existing ships. So Henry V had both royal vessels and a large requisitioned set of ships for his invasions of France, in 1415 and 1417, but the royal ships had disappeared from the record by a few years after his death. Edward IV (1461–1470, 1471–1483) had to begin again, and during his reign he acquired several ships. He maintained the ships long enough for them to require a separate administration, and this has entitled Edward to be considered the founder of the Royal Navy – though this is a title generally awarded to his grandson Henry VIII, among others.

Some of Edward’s ships survived until Henry’s reign, but from the time of Henry VII (1485–1509) it became increasingly normal for kings to have ships built. One reason was the growth of specialization into heavily armed warships. Merchant vessels could not easily be converted, especially if their requisitioning was done in an emergency. But to build, and still more to maintain, a navy was expensive. The Scottish King James IV (1444–1513) built two great warships, the Margaret (700 tons) and the Michael (1,000 tons), which he could not afford to keep up and handed over to France, from whom they were captured by Henry’s navy in 1488 and 1490.