Lord Henry Seymour was a younger son of Edward Seymour, 1st Duke of Somerset

Edward Seymour, 1st Duke of Somerset

Edward Seymour, 1st Duke of Somerset, 1st Earl of Hertford, 1st Viscount Beauchamp of Hache, KG, Earl Marshal was Lord Protector of England in the period between the death of Henry VIII in 1547 and his own indictment in 1549....

 and Anne Stanhope

Anne Stanhope

Anne Seymour, Duchess of Somerset was the second wife of Edward Seymour, 1st Duke of Somerset, who held the office of Lord Protector during the first part of the reign of his nephew King Edward VI, through whom Anne was briefly the most powerful woman in England...

. Aboard HMS Rainbow

HMS Rainbow (1586)

RainbowThe 'HMS' prefix was not used until the middle of the 18th century, but is sometimes applied retrospectively was a galleon of the English Royal Navy, built at Deptford Dockyard by Peter Pett , and launched in 1586...

 he commanded the 'Narrow Seas' Squadron of ships that took part in the Battle of Gravelines against the Spanish Armada

Spanish Armada

This article refers to the Battle of Gravelines, for the modern navy of Spain, see Spanish NavyThe Spanish Armada was the Spanish fleet that sailed against England under the command of the Duke of Medina Sidonia in 1588, with the intention of overthrowing Elizabeth I of England to stop English...

 in 1588. Controlling the seas off Dunkirk they joined the main British fleet (the 'Western Squadron') near Calais

Calais

Calais is a town in Northern France in the department of Pas-de-Calais, of which it is a sub-prefecture. Although Calais is by far the largest city in Pas-de-Calais, the department's capital is its third-largest city of Arras....

 on 6 August, adding about a third to the total size.
Married Joan Percy, daughter of Thomas Percy, 7th Earl of Northumberland

Thomas Percy, 7th Earl of Northumberland

Blessed Thomas Percy, 7th Earl of Northumberland, 1st Baron Percy, KG , led the Rising of the North and was executed for treason. He was later beatified by the Catholic Church.-Early life:...

.