In 1806, aged 14, Williams entered the Royal Navy, serving on HMS Barfleur.
He became a midshipman in 1807.
He then served on HMS Maida under Captain Samuel Hood Linzee during the Battle of Copenhagen when the Danish fleet was seized in 1807.
He landed with the party of seamen who manned the breaching battery before the city.
He participated in the engagement on 13 February 1810, when 8 boats under the command of Lieutenant Gardiner Henry Guion, attacked nine French gun boats in the Basque Roads.

On HMS Galatea, under Captain Woodley Losack, he took part in the Battle of Tamatave (1811) between three English frigates, under the command of Captain Schomberg, and three French vessels of superior force.
Williams was wounded and never entirely recovered.
 For this service he qualified for the Naval General Service Medal, which was awarded in 1847 with clasp "Off Tamatave 20 May 1811".

After the outbreak of the War of 1812 between Britain and the United States, he served on HMS Saturn as part of the blockading squadron off New York City.
He was transferred to HMS Endymion and served under Captain Henry Hope in the action on 14 January 1815 against the American warship USS President.
When the latter was forced to surrender, Williams was a member of the small prize crew that sailed the badly damaged vessel to port, after riding out a storm and quelling a rebellion of the American prisoners.
In 1848 the Admiralty authorized the issue of the Naval General Service Medal, with clasp "Endymion wh.
President", to any still surviving crew from Endymion.

Before serving on HMS Saturn, Williams sat and passed his examinations for the rank of lieutenant, although he was not promoted to lieutenant until 28 February 1815, after the Treaty of Ghent was ratified by the United States.
When peace came in 1815, he retired on half pay.
 At the age of 23 he had been "in the North Sea and the Baltic, around the French and Spanish coasts, southwards to the Cape, up to the eastern shores of Madagascar, across the Indian Ocean to Mauritius, and northward to the coast of India.
After service at Madras and Calcutta, it was on into the cold American winter and that epic last naval engagement in which he took part, on the Endymion".

Williams' experiences during the Napoleonic Wars and the War of 1812 influenced his decision to become a Christian missionary and peacemaker in carrying out the work of the Church Missionary Society in what was then considered an isolated and dangerous mission in Aotearoa (New Zealand).
In 1806, aged 14, Williams entered the Royal Navy, serving on HMS Barfleur. He became a midshipman in 1807. He then served on HMS Maida under Captain Samuel Hood Linzee during the Battle of Copenhagen when the Danish fleet was seized in 1807. He landed with the party of seamen who manned the breaching battery before the city. He participated in the engagement on 13 February 1810, when 8 boats under the command of Lieutenant Gardiner Henry Guion, attacked nine French gun boats in the Basque Roads.
On HMS Galatea, under Captain Woodley Losack, he took part in the Battle of Tamatave (1811) between three English frigates, under the command of Captain Schomberg, and three French vessels of superior force. Williams was wounded and never entirely recovered.  For this service he qualified for the Naval General Service Medal, which was awarded in 1847 with clasp "Off Tamatave 20 May 1811".
After the outbreak of the War of 1812 between Britain and the United States, he served on HMS Saturn as part of the blockading squadron off New York City. He was transferred to HMS Endymion and served under Captain Henry Hope in the action on 14 January 1815 against the American warship USS President. When the latter was forced to surrender, Williams was a member of the small prize crew that sailed the badly damaged vessel to port, after riding out a storm and quelling a rebellion of the American prisoners. In 1848 the Admiralty authorized the issue of the Naval General Service Medal, with clasp "Endymion wh. President", to any still surviving crew from Endymion.
Before serving on HMS Saturn, Williams sat and passed his examinations for the rank of lieutenant, although he was not promoted to lieutenant until 28 February 1815, after the Treaty of Ghent was ratified by the United States. When peace came in 1815, he retired on half pay.  At the age of 23 he had been "in the North Sea and the Baltic, around the French and Spanish coasts, southwards to the Cape, up to the eastern shores of Madagascar, across the Indian Ocean to Mauritius, and northward to the coast of India. After service at Madras and Calcutta, it was on into the cold American winter and that epic last naval engagement in which he took part, on the Endymion".
Williams' experiences during the Napoleonic Wars and the War of 1812 influenced his decision to become a Christian missionary and peacemaker in carrying out the work of the Church Missionary Society in what was then considered an isolated and dangerous mission in Aotearoa (New Zealand).
Henry Williams (missionary)