James VI died on 27 March 1625. When looked at from a naval perspective, the reign of his son, Charles I, splits into three parts: first, conducting a war against both Spain and France from 1625 until 1630; then refashioning the English navy through the construction of the ship money fleet; and finally that force's failure and betrayal in the civil wars. For Scots these three phases were equally distinct: a failed attempt at creating a royal Scottish navy in the first; the question of their place in the sovereignty of the British seas that the ship money fleet was supposed to enforce in the second; and thirdly how to deal with that fleet as an enemy in the Bishops’ Wars.

Charles was the last monarch born in Scotland but was generally less interested in the matter of Anglo-Scottish union than his father had been. The exception was religious conformity, which was to be achieved by pushing the English model onto the other two kingdoms, the complexities of which would blow open broader constitutional issues. In the naval sphere, the pursuit of sovereignty of the British seas had obvious unionising aspects, but implementation often lacked British thinking. Contrariwise, the creation of a royal Scottish navy, at first glance a move away from union, aimed at maximising the naval potential of the British monarchy as a whole, which might be said to be a unionising ideal. This did not get very far; the navy's failure was of a piece with a Scottish war effort that was ‘feeble and under-financed’.

Spanish War, Spanish Union

Charles left Madrid having failed to procure a Spanish bride and intent on restitution of the Spanish-occupied Palatinate by war; Charles and Buckingham also got initial support from the English parliament for an anti-Spanish naval war. An expedition dispatched in October 1625 landed at Cadiz, but it soon became chaotic when some wine was discovered and promptly drunk. The Flota treasure fleet from the Americas was missed, and the fleet was ravaged by storms and disease on its homeward voyage.

The situation was further complicated by the outbreak of war with France in 1627. France had been courted to open a route to the Palatinate, and so Charles had married Henrietta Maria, youngest sister of Louis XIII.