Acasta Class Destroyer (1912)

Twenty destroyers of the Acasta Class (redesignated the "K" class in 1913) were completed as part of the 1911-1912 Programme. Twelve were Admiralty design, and eight were Specials.

They were the first Royal Navy destroyers to drop the 12-pdr gun and use only 4-in guns, increasing to three such weapons from two although the third only had 35 degrees of firing arc on each beam.

At the outset of the war, these ships comprised the Fourth Destroyer Flotilla under leader Swift.

Overview of 20 vessels
Citations for this data available on individual ship pages
Name	Builder	Laid Down	Launched	Completed	Fate
Acasta	John Brown & Company		10 Sep, 1912		May, 1921
Achates	John Brown & Company		14 Nov, 1912		May, 1921
Ambuscade	John Brown & Company		25 Jan, 1913		Sep, 1921
Christopher	Hawthorn Leslie & Company		29 Aug, 1912		May, 1921
Cockatrice	Hawthorn Leslie & Company		1912		May, 1921
Contest	Hawthorn Leslie & Company		7 Jan, 1913		Torpedoed 18 Sep, 1917
Shark	Swan Hunter		30 Jul, 1912		Sunk 31 May, 1916
Sparrowhawk	Swan Hunter		12 Oct, 1912		Sunk 1 Jun, 1916
Spitfire	Swan Hunter		23 Dec, 1912		May, 1921
Lynx	London & Glasgow		20 Mar, 1913		Mined 9 Aug, 1915
Midge	London & Glasgow		22 May, 1913		Nov, 1921
Owl	London & Glasgow		7 Jul, 1913		Nov, 1921
Hardy	John I. Thornycroft & Company		10 Oct, 1912		May, 1921
Paragon	John I. Thornycroft & Company		21 Feb, 1913		Torpedoed 18 Mar, 1917
Porpoise	John I. Thornycroft & Company		7 Jul, 1913		Mar, 1921
Unity	John I. Thornycroft & Company		18 Sep, 1913		Oct, 1922
Victor	John I. Thornycroft & Company		28 Nov, 1913		Jan, 1923
Ardent	William Denny & Brothers		8 Sep, 1913		Sunk 1 Jun, 1916
Fortune	Fairfield Shipbuilding and Engineering Company		17 Mar, 1913		Sunk 31 May, 1916
Garland	Cammell Laird		23 Apr, 1913		Sep, 1921

Electric Logs

It was ordered that these ships were to receive two Trident Electric Logs and one Charthouse Receiver sometime prior to March 1914, but the delivery date is unknown.

Performance

The first ships completed steered very poorly.

Acasta took so long to turn through 8 points that only Mohawk, which was 10 feet longer, was slower to effect this. Her advance of 596 yards was larger than all but those of 4 "Tribals". Acasta's diameters were 861 yards to starboard and 1097 to port — nearly twice that of the Acheron class's Yarrow special Firedrake.

Things were so bad that comparative turning trials were ordered for Firedrake (rudder area 41.75 square feet) and Christopher (46 square feet). The issue was seen that a slight advantage for Christopher in radius at lower (385 yards at 20 knots) fell apart at higher speeds (960 yards at 29 knots versus 490 yards for Firedrake). The Acasta class advance was worse at all speeds (295 versus 280 yards at 16 knots, degrading to 605 versus 375 at 29 knots). It was determined that Christopher's response to additional helm disappeared past 20 degrees of helm, and further rudder seemed to actually worsen diameter up to 28.5 degrees and advance to 26 degrees at which point the rudder again became helpful. She achieved her best diameter (785 yards) at 20 degrees helm, where her sister Achates had a whopping 1808 yards diameter.

The suggestion was offered that the shape of the stern might be causing the problem, but a larger rudder or one with a plate on top of it were offered as less costly fixes than rebuilding the sterns. The plate was chosen, but though the forensic trail goes cold, it seems something effective was done, as Midge, Lynx and Owl had a reasonable 700 yard diameter at 33 knots.

Ardent was most economical, burning 12.9 tons per hour. The average was 15.4 tons per hour. With her semi-geared turbines, Garland burned 13.2 tons per hour, or 2.307 miles per ton as opposed to just under 2 miles per ton for the direct-drive turbines in the other ships.

On gun trials in rough conditions, it was found that the centre 4-in gun fouled the torpedo tube and enjoyed firing arcs of only 35 degrees.

Armament

Some of the ships were required to land their aft gun to accommodate depth charges.

In late September, 1914, the Admiralty ordered that the guns on the Tribals and later classes were to be given loading lights, initially on temporary circuits.

4-in Guns (First 13 Ships)

The first ships carried their 4-in guns on P. VII mountings.

The mounting could elevate 20 degrees and depress 10 degrees, but its sight could only elevate 15 degrees and the range dial to 15 degrees (8,500 yards). It recoiled 38 inches.

These gear-worked sights had gearing constants of 26.67 and range dials for 2275 fps, and 1-in and .303-in aiming rifles. M.V. could be corrected by a cam pointer allowing for a decrease to 2075 fps.

It is unknown whether these were F.T.P. sights.

The deflection gearing constant was 57.20 with 1 knot equal to 3.05 arc minutes, corresponding to 2275 fps at 2000 yards. Drift was corrected by inclining the sight about pivot pins 2 degrees.

The layer's sight line was 12.5 inches above the bore, and 21.45 inches left. The trainer's telescope sight line was 12.5 inches above and 17.4 inches right.

The sight had neither a temperature corrector nor a "C" corrector.

Both sides had an open sight.

Immediately before the war, a project to test "5 degree elevating gear" in Cockatrice, Shark and Sparrowhawk that had stalled for some time when parts had been incorrectly machined was being expedited. I would think that this gear was meant to provide sight elevations to match the mounts' limits of 20 degrees. The gear was issued three weeks later (to Acasta, Achates and Christopher as well), and reports were requested on by the end of the month – a measure of the imperative of the war that had just started.

4-in Guns (Last 7 Ships)

Garland, Paragon, Porpoise, Unity and Victor, at least, carried three 4-in Q.F. Mark IV guns on P. IX mountings as in the following "L" class destroyers. The remainder of this section is copied from our section for the "L" class.

There were 120 rounds per gun.

The mounting could elevate 20 degrees and depress 10 degrees, but its sight could only elevate 15 degrees and the range dial was actually only graduated to 12.5 degrees (7,900 yards). "This was soon remedied by the supply of additional sight strips graduated to the extreme range of 10,200 yards." A photo of a weapon from H.M.S. Lance on museum display shows that the range dial's markings to 10,200 yards required it to rotate through about 440 degrees – a revolution and a half. That is, the range graduations were helical.

These gear-worked sights had gearing constants of 26.66 and range dials for 2200 fps, and 1-in aiming rifle, though at least one was marked for 0.303 aiming rifle on its reverse. M.V. could be corrected by a cam pointer allowing for a decrease to 2000 fps.

Unlike some P. IX sights, these were not F.T.P. sights. The museum piece alluded to above shows that the range and deflection receivers were not even particularly convenient in their location.

The deflection gearing constant was 52.6 with 1 knot equal to 3.18 arc minutes, corresponding to 2200 fps at 2000 yards. Drift was corrected by inclining the sight about pivot pins 2 degrees.

The layer's telescope sight line was 12.5 inches above the bore, and 21.45 inches left. The trainer's telescope sight line was 12.5 inches above and 17.4 inches right. Open sights were 13.3 inches above the bore and 24.35 inches left for layer and 20.3 inches right for trainer.

The sight had a temperature correcting scale plate and a "C" corrector.

The layer had an open sight. The trainer's sight could be used as a free sight with a counterweight.

During the war, some of the ships were required to land their aft gun to accommodate depth charges.

As the midship 4-in mounting could train in a full circle and thus might break the electrical firing circuit wires, in June 1914 it was ordered that the pedestal to these guns have a warning plate fitted to them reading, "See circuits clear when training across limit stops."

In late September, 1914, the Admiralty ordered that the guns on the Tribals and later classes were to be given loading lights, initially on temporary circuits.

Other Guns

In September 1916, Garland tested a P. IX trap-door mounting that could elevate a 4-in Mark IV gun 50 degrees in 1 minute 50 seconds. Acasta and possibly some other ships also received this, probably on the midships or aft gun, although Acasta later surrendered hers in favour of an enhanced torpedo outfit. Other units had a single 2-pdr pom-pom by 1920.

Doodling

In a gun test for the forward gun using a whip hoist below and manual handling otherwise, one man in the magazine, one in shell room, one on the upper deck platform and one on the forecastle could supply 3 boxes of ammunition and 12 shells to the racks in two minutes. The mid and aft guns without a hoist could do three boxes and 9 shells in 50 seconds.

Torpedoes

• two single 21-in tubes on the centreline

The height of the foremost tube above the deck required them to have a foldable platform pivoted on the stokehold to position abaft the tube to assist in "launching in" (loading) the torpedo. This platform could be swung to either side of the deck and were high enough to pass over any spare torpedoes stored on the chocks. Concerns of visibility prompted instructions that provisions be made to guarantee clear arcs of 65 degrees to each side of the beam for the torpedo directors.

In June, 1918, Acasta replaced her tubes with a double mounting Mark III another double Mark IV, losing her after gun, trap door mounting and searchlight.

Other Weapons

Early in 1918, Cockatrice was fitted with depth charge throwers and rails capable of dropping 5 charges at 3 second intervals.

Addition of depth charges to these ships required some of them to land their aft gun.

Other Equipment

In October 1914, as the Acastas were all serving in the Fourth Destroyer Flotilla, they were ordered to have the (hydraulic?) searchlight control system first used in H.M.S. Badger fitted.

Unity successfully tested an observation balloon in April 1918. It was towed while escorting a convoy at 13 knots (40 knot wind speed at balloon) at an altitude of 300 feet. It could be hauled down and up in as little as two to five minutes, eventually by moving the winch to the pom-pom platform from which crew could be easily exchanged. 842 miles of patrols were carried out with little need to refill the balloon.

In January 1918, Garland landed her midship tube and 4-in gun for a 24-ton lined acid tank for a smoke-generating apparatus. The acid was vile and ate iron and steel, requiring the decks to be washed with 2 percent soda ash solution after each smoke making use. Paintwork disappeared on first use. The acid produced intense heat and dense white smoke when the acid contacted sea water. About one quarter ton to one ton of acid per hour was used. It was impossible to use with a following wind and people abaft the funnel had to wear a gas mask. The system needed improvement, but was so effective that it was used at the Zeebrugge Raid.

Fire Control

By 1915, at least, these ships also had fixed voice pipes installed between decks with the last lengths being flexible (one voice pipe for gunnery, one for torpedoes) fitted between bridge and guns, torpedo tubes, and searchlights. A third voicepipe, entirely flexible, ran from bridge to the forward gun.

Instruments

By 1920, the ships in Acorn to Laforey classes had Wise Pressure Telegraphy Systems in place to support fire control.

Rangefinders

A 1-m base rangefinder was supplied to all destroyers of the "Tribal" class through "L" class around 1916, but this was later withdrawn.

Torpedo Control

Electrical Instruments
found in most or all "Acasta" class destroyers

A single sighting position was located high up in the centre of the bridge, thus requiring only a single set of firing pushes or keys as well as keys for operating a buzzer at the forward torpedo mount and a rattler at the aft mount.

The data instruments used were electrical. A single Mark I deflection transmitter at the control position, and separate order transmitters and keys, one for the forward tubes and one for the aft. Each torpedo mount had a combined receiver for these signals.

See Also

• Wikipedia

Bibliography

• Gray, Randal (editor) (1985). Conway's All the World's Fighting Ships 1906–1921. London: Conway Maritime Press. (on Amazon.com and Amazon.co.uk).
• March, Edgar J. (1966). British Destroyers: A History of Development, 1892-1953. London: Seeley Service & Co. Limited. (on Bookfinder.com).
• Admiralty, Technical History Section (1920). The Technical History and Index: Alteration in Armaments of H.M. Ships during the War. Vol. 4, Part 34. C.B. 1515 (34) now O.U. 6171/20. At The National Archives, Kew, United Kingdom.