There was only one "ultimate deterrent" in the 19th Century - the Royal Navy. The greatest military force of its day, only the armies of the Czar came anywhere near it in popular imagination. The phrase "gunboat diplomacy" still reminds us of the solution of many Victorian statesmen to overseas political problems.
Apart from supplying Naval Brigades to assist the Army ashore - most significantly in the Crimea, the Indian Mutiny and the Anglo-Boer War - the occasions when the Victorian Navy actually fired its guns in anger between 1837 and 1914 were few.
To support the Turkish Government against Mehemet Ali of Egypt, it bombarded Acre in 1840. In the Crimean War, it fought the Russian Navy not only in the Black Sea but also in the Baltic, the Arctic (where it attacked the Russian whaling fleet) and the Pacific. Finally, in 1882 the Mediterranean Fleet bombarded Alexandria when forces opposing the pro-British ruler of Egypt would not disarm the forts guarding the harbour.
On a smaller scale, HMS Shah, flagship of the British Pacific Squadron fought a ship-to-ship action with the Peruvian armoured turret ship Husacar which had been hijacked by rebels and seemed likely to turn pirate. Then, on its way home, the Shah was diverted to South Africa where the ship's company took part in the Zulu War of 1879. Probably only in the Victorian Navy could a man say that he had fought against an enemy armed with the latest in modern scientific weapons and also against warriors armed with spears and shields.
However, the Royal Navy's greatest fight, both in terms of numbers of ships and men involved and the sheer geographical area covered, was against the Slave Trade. Slavers operated on both on both the West and East Coasts of Africa - from which the tragic human "cargo" were sent to the plantations of America or the domestic slavery of the Persian Gulf.
Facing death from fever, professional ruin - for the officers at any rate - if they overstepped the bounds of International Law and well-armed and desperate crews on the slave ships, the Royal Navy put a major effort into what the Victorians rightly saw as a great humanitarian crusade. In addition, the Royal Navy also carried on the vital but unspectacular task of surveying the globe. Not only were navigational charts prepared but, more importantly, they were made freely available to seafarers of all nations.
As part of this survey work, in 1845 Captain Sir John Franklin RN led an expedition in HM Ships Erebus and Terror to try and complete the North West Passage from the Atlantic to the Pacific. Neither he nor his crews were ever seen again and over the following ten years (until the Crimean War put a stop to them) numerous expeditions were dispatched to search for the missing ships and men in what is one of the great epics of British naval history.
When Victoria became Queen in 1837 the Royal Navy consisted of sailing ships firing broadsides, much like those of Trafalgar, although larger and with auxiliary steam engines.
From these wooden walls, the Navy progressed through "ironclads" like HMS Warrior of 1860, early experiments with gun turrets (one of which - HMS Captain - was disastrous; she capsized in 1870 and is the only British battleship lost because she was unseaworthy), breach loading guns, torpedoes, wireless and turbine engines, until by 1914 the Navy had evolved the huge steel battleships that formed the Grand Fleet under Admiral Jellicoe.
The Victorian Navy was a unique institution. We shall never see anything like it again.