18-in Mark IV Torpedo (UK)

The 18-in R.G.F. Mark IV Torpedo was a British torpedo developed at the Royal Gun Factory in 1894 or 1895.^{[Fact Check]} Over 1,000 were produced.

Development and History

In 1895, they were just about to enter service.

Mark IV

The final design is extensively laid out in the Annual Report of the Torpedo School, 1895.

The construction was very similar in materials to the 14-in Mark IX torpedo.

• Diameter: 17.71 inches
• Length: 16 feet, 7.4 inches
• Weight with pistol, without air: 1,156 pounds
• Metacentric height: at least .575 inches
• C.G. distance from tip of shaft, no air: 114.175 inches
• C.G. distance from tip of shaft, 60 pounds air: 114.35 inches
• Warhead: 200 pounds wet guncotton

It carried a charge of 170 pounds, 15 ounces – the same as in the 18-in Mark III torpedo.

It had a Brotherhood engine of 3.25x3 inches.

Mean pitch of propellors was 40 inches. When charged with air, the torpedo must pass through a gauge 9 inches long and 17.725 inches internal diameter.

With pistol and charged with 60 pounds of air was ballasted and adjusted to float horizontally and upright in salt water at a density of 1.026 and 60 degree temperature. In fresh water, with pistol and no air, it had a buoyancy of 31 pounds.

The proof and passing tests were six runs when charged to 1,350 psi:

• two runs from a submerged frame at target 800 yards distant
• two runs from an A.W. tube at least four feet above the water at a target 400 yards away
• one run above water at target 800 yards away
• one run from submerged frame at target 800 yards away

The limits of deviation permitted were:

• lateral deviation from the submerged frame must be less than 12 yards either way throughout run
• from A.W. tube, lateral deviation of 8 yards at 400 yards or 24 yards at 600 yards
• deviation from set depth not to exceed +/- 18 inches

The speeds required were:

• not less than 30 knots to 600 yards and 29 knots to 800 yards in 60 degrees and warmer
• not less than 29.5 knots to 600 yards and 28.5 to 800 yards in 50-60 degrees
• at least 29 knots to 600 yards and 28 knots to 800 yards in water colder than 50 degrees

Endurance was tested in just one torpedo in a batch of twenty, after passing the above tests:

1. make six short runs from above water gun 10 feet or more above water
2. be fired from submerged frame and pass within 14 yards of target at 800 yards
3. it must then "shew no signs of weakness or distortion"

Mark IV H.

A late surprisingly late variation for such an early Mark, it was conceived 1916, it used the Mark VI* H. engine and had a warhead of 250 pounds Amatol. It was projected to deliver 35 knots to 1,500 yards.

Manufacture and Use

Horsea was adjusting the first manufactured lots in 1896:

• 89 newly built torpedoes with Side Lugs made 30.47 knots at 600 yards and 29.08 knots at 750 yards in 53.1 degree water.
• 128 newly built torpedoes with Hook Brackets made 28.72 knots at 600 yards and 27.23 knots at 750 yards in 55.4 degree water.
• one short R.G.F. torpedo of unstated Mark was also tested, achieving 28.64 knots to 600 yards in 42 degree water.

1905

In 60 degree water, 18-in H.B. torpedoes of Mark I* through IV were approved for the setting of 1,500 yards at 20.25 +/- 0.25 knots at 1,400 pounds pressure. The S.L.L.R. torpedoes of the same Marks did at 21.75 knots to 1,500 yards and the S.L.S.R. models 25.25 knots at 1,350 pounds pressure.

1918

30 of 1155 remaining H.B. Mark IV and Mark IV H. torpedoes were broken up in 1918.

1919

In 1919, it was approved to break up 680 Mark IV H.B. and S.L. torpedoes, to leave 468 remaining.

See Also

• 14-in Mark IX torpedo, its contemporary