The Navy is presently involved in acquiring & “low cost” antiship torpedo for submarine use. It would therefore seem useful to recall World War II submarine experience with “steam” (now known as “thermal”) torpedoes and “electrics.”
The U.S. started the war with Mk 10 and Mk 1~ stean, torpedoes — with the Mk 14 later converted to the Mk 23 by primarill1 eliminating the Mk 14 ‘s low speed feature. By late 1943 the batterypowered Mk 18 “electric” torpedo appeared in the operating submarine forces. In 1944, 30% of all torpedoes fired were Mk 18s, but by 1945 far greater numbers of Mk 18s were being used than Mk 14s and 23s. The ~~ 14s cost over $10,000 per copy, while the more easily produced ~~ 18 was casted at about $2,500 each, and being supplied at 300 per month in late 1944.
A brief rundown on the character of these antiship torpedoes shows:
- The Mk 10 torpedo — a carryover from WW 1 developement — used steam turbines powered by the combustion of air and alcohol with a water spray injected into the combustion pot to form steam to run the turbines. The exhaust from the turbines was then dumped overboard, creating a visible wake behind the torpedo. The Mk 10 made 36 knots, had a 485# torpex warhead and ran 3500 yards.
- The Mk 14 was a similar “steam” torpedo of 46 knots speed, 4500-yard range, a 668# torpex warhead and with a Mk 6 exploder, (the main troublemaker through the early years of the War).
- The Mk 23 was similar to the Mk 14 but had the Mk 14 1s low speed feature, of 31 .5 knots speed and 9000-yard range, eliminated.
- The MK 18 was a quiet, wakeless electric torpedo with a simple contact exploder -fashioned after the German electric torpedo captured in 1942. The Mk 18 made 29 knots when at about 70°F battery temperature. However, and not clearly understood by early users of this weapon, when the torpedo batteries were at a low temperature on firing, the speed was likely to be several knots lower then expected. This resulted in — at that time — unexplained misses. Its warhead held over 600#s of explosives similar to the Mk 14, and its range was 4500 yards. ~~ improved electric, the Mk 46 made 45 knots, using a silver electrode and seawater electrolyte and was in production by the end of the War.
The World War II u.s. experience with steam torpedoes highlights certain shortcomings of noisy, wake-making torpedoes when fired against surface ships — whether escorted or not. Fired at ships in daylight, the wakes were likely to be seen — with warships taking rapid evasive action and merchant ships sounding an alert which · frequently caused convoys to be zigged away preventing a follow-on submarine attack. At the sante time. the rapidity and accuracy of counterattacks as a result of sighting the wakes put the firing submarine at considerable hazard because its position was easily established for both the warship escorts and escorting aircraft. When firing steam torpedoes at ships in shallow waters the submarine was doubly in jeopardy because of its restricted mobility in evading a pin-pointed rapid counter attack.
Some examples from u.s. submarine patrol reports can serve to illustrate these observations:
- S-37″s sixth war patrol, 1942: “at 2300 sighted a raiding party of 4 DDs in column and two heavy ships on their quarter — the “Bougainville express.” Closed for a 90°track shot on the lead destroyer. Range 1200 yards on firing. Mk 10 fish were evidently spotted, as DDs promptly zigged away, then headed back at S-37 and carefully placed 16 depth charges, close, (only 2 seemed far off).”
- SEADRAGON’s fifth war patrol, 1942: “A DD was seen searching for SEADRAGON. Earlier her periscope had probably been spotted by a large force that passed over SEADRAGON. An undetected approach on the DD was made and three Mk 14s fired. The first torpedo was observed to be making a good trail of smoke (it might have had its smoke ring missing). It was spotted quickly by the DD which swung to miss all 3 torpedoes. Then the DD charged back at SEADRAGON with some charges very close — 3 per string. A 4-motored plane followed up with depth charges on SEADRAGON’s slick.”
Six days later: “Spotted a small freighter with minelayer escort. At 1500 yards, fired 3 Mk 14s and got one hit. Within a minute, depth charged by minelayer with a good close pattern. Freighter was observed being taken in tow by minelayer as bombers kept dropping occasional bombs near SEADRAGON’s periscope.”
Four days later: “SEADRAGON’s bridge watch sighted the wake of a torpedo and SEADRAGON was tm·ned ~.harply away. One fish was sighted missing ahead.” (The Japanese used “thermal n wake-making torpedoes, as well.)
Six days later: “4 tubes were rnade ready and 3 Mk g t.orpedoes had been fir·ec.i at a Jap sub when SEADRAGON caught a bomb from an escorting aircraft, doing consider~ble damage and cau~dng the 4th torpedo tc1 be jammed halfway out of the tube.”
Four days later: Fired 4 torpedoes at a transport, escorted closely by two DDs. Immediately after a hit was made, a DD t-1as ovet· SEADRAGON laying depth charges in accurate strings, SCJIJle of \lt>ich shattered light bulbs, broke gauges, etc.”
- o CREVALLE’s third war patrol, 1944: “Lined up on a huge tanker, fired 6 Mk 14s and got 3 hits. Two bon.1bs hit close aboar·d CREVALLE during firing. The fir~t. bon•b l-Ift.~ believed aimed at tbe wakes of 1’j ~1h just launched. Over 60 depth charges were heard in the first rush, with the depth charging ~tar·ting almost itlu;ediately ~rith the launch of the 6th fish. All charges were very close except for· one which sounded fairly far away.”
- o HARDER’s fifth war patrol, 1944: “All six Mk 23s r;d ssed. Target apparently saw their wakes and was olJ~er·,,c~c: tc zig sharply away causing last 4 to miss, (first two were observed to be erratic).
- o REDFISH first, 1944: “Two Mk 23 torpedoes were observe.d to be running nicely but putting up 8 terrifj_c smoke trail. The torpe<.io<w \o.·ert~ almost at their 2 AK tarsets in a J • rL<‘ Qonvoy, when stearr tJr::« (‘·b.t;erved coming from the whistle of one of them. (This indicated a single-toot which warned the rest of the convoy that the ship wa.s being attacked from the starboard side. Frequently with such a warning, the entire convoy would be zig~ed away, preventing the low-mobility conventional submarine from getting in a second torpedo attack.)
A few days later: “Made a periscope attack on 4 ships plus 3 escorts. At 1515 fired 4 Mk 23s at large tanker then let go 3 false target shells as REDFISH was taken deep. At 1517 heard two hits and a minute later felt 56 depth charges — the first 25 dropped apparently on the false target shells, so they weren’t very close.” (The use of evasion countermeasures highlighted here shows their necessity due to great rapidity of counterattack stemming fronc a good knowledge of the firing submarine’s location.)
- SHARK II’s first war patrol: “Mk 23 torpedoes were again seer• tt’ leave a bh:ish colored smoke alc•ne. tbejr wakes. 1730, sixth torpedo hit the leading freighter. 1732 first pattern of 10 depth charges. All close.
- GUARDFISH’s eighth: “At 0746 heard a timed hit on second ship. Everyone in our sub heard one of our •~ 23s pass down on starboar·d f:lclfl C~nd cross over the rJaneuvering room. This must have been our #3 torpedo making a circular run. At 0749 the first of many depth charges. Two shook the boat considerably.”
The experience of U.S. submarines using the Mk 18 torpedoes was somewhat different:
- CROAKER’s first, 1944: “Four •~ 18 stern torpedoes fired at a ranee of 800 yards. All missed. All torpedoes pr·obably ran under, and the 3500-ton merchant ship “sailed uncon cernedly on its way, as likewise did the 4 electrics.”
A day later: “A KUMA class cruiser was attacked submerged with four electrics. A lucky zig of the cruiser made it blunder into one of the invisible fish, which hit in the cruiser’s stern and sank her.” (Note that a good ASW warship was unaware of the torpedo attack.) In summary: “Preference in the issue of Mk 18 torpedoes is given to submarines operating in areas where daytime attacks only are likely to be undertaken.”
- SUNFISH’s fifth: “Five Mk 18s were chosen (from a mix of 18s and 23s) for this daylight attack with 4 hitting a gunboat and a medium freighter in a convoy of 5 merchant ships and 3 escorts. A minute after hearing two loud torpedo hits took twelve close depth charges.”
- SPADEFISH’s first: “In a periscope attack, fired four Mk 1Bs at a MUTSUKI class DD. All missed. No evidence DD detected the torpedoes.” Later: “A DD passed ahead. In the glassy sea he would have spotted the Mk 23s remaining, in time to avoid.”
- A bulletin of Ordnance Information Report 145 noted that on one patrol, “A full load of Mk 18-1 torpedoes were carried on this patrol. 23 of those were fired at enemy targets and as far as is known, all ran “hot, straight and normal.” Would prefer to carry them rather than Mk 14s or 23s.”
- DRUM’s 11th: 26 October, 1944. 0357, “fired four stern Mk 18-1s at 4000-ton freighter. Got 3 hits. Escort on bow of target did not chase us.” Later at 0637. “Daylight submerged attack. The ships are now zigging every three minutes. In the next 15 minutes we shifted targets four times.”
- SEADRAGON’s 7th: 24 October, 1944. 1055, “day submerged attack. Fired four Mk 1Bs, got 2 hits. Sank an AK of 5000 tons. CHIDORI escort at 1101 dropped first of 8 depth charges, not too close.” Later, at 1214 fired four Mk 18s at range of 1000 yds. Observed 3 hits. Ship sank in less than two minutes.” 1218, “first of 15 depth charges from CHIDORI escort. None too close.” Later, 1404, “submerged attack. Fired four Mk 18s at 4000-ton AX. 2 hits. CHIDORI on short scale. 1405, first of 25 depth charges. None too close.”
- TANG’s 5th: 11 October, •44. “in fact, the perforrnMtoe of the first twenty-three Mk 18-1s in all runnit1g perfectly, with 22 hits, attest to this.” (The 24th was a circular run which sank TANG.)
- BARB’s 10th: 15 November, 1944. 2336, “fired six bow Mk 18-1s at SHOKAKU class aircraft carrier with 4 destroyer escorts, torpedo run 3500 yards. One hit, as target zigged about 3 minutes after firing.”
- GREENLING’s 11th: 0939, 10 November, 1944, “Day periscope attack on WAKATAKE class DD. Fired four Mk 18-1s, one hit. Destroyer did r.ot counter attack. Lost depth control and did not see the DD sink.”
- PINTADO’s 3rd: November 3, 1944. 2150, “night submerged attack \lith six Mk 18-1s on. SHOKAKU class aircraft carrier, escorted by several DDs. 4 hits, two in carrier and tl-lo in TERUTSUKI class DD. Saw DD blow up and sink. Aircraft carrier damaged.”
- ATULE’s 1st: 0505, 20 November, 1944. “Fired 4 stern Mk 18-1s, 2540 range, at HATSUHARA class DD. One hit. 2 1/2 minutes later his stern went under.” Later, on 27 November·, “On only the submel~ged attack, the first, was there any counter action.”
As to how the Mk 18 performed relative to the Mk 14s or 23s, a box score of hits versus torpedoes fired — by submarines returning to Pearl Harbor in June, 1944 — showed the following results: of some 83 Mk 1~s and 23s fired, 31 were assessed as hits. Whereas, of the 47 Mk 18s fired, 14 were assessed as hits. This gave the Mk 14/23 torpedoes about a 36J hitting probability as against the Mk 18s 30J. It was observed from a reading of a few of the patrol reports that where there was a choice, the Mk 18 was used for daylight submerged attacks. That, plus its slower speed and possibly its running slower than expected may partially account for the lower percentage of hits achieved. The slow speed of 29 knots would cause more misses against zigging targets; and the poorer tracking data and timing of firing as experienced in periscope approaches might also account for some of the disparity. But more study of patrol reports appears necessary to give good definitive answers to the difference in hit probability observed for this small segment actually tabulated.
It should be recalled that u.s. submarines were fitted with a simple torpedo-warning-device consisting of four small sonar listening heads implanted in the outer hull which covered all four quadrants. The loud enemy torpedoes, it was felt, should be detected sufficiently far off to allow for effective evasive maneuvers by the u.s. submarine shot at.
Today, noisy torpedoes which leave either a wake-trail or produce an infrared scar on the surface of the ocean should be readily detected by greatly improved surface and air ASW forces. Use of infrared binoculars to spot thermal torpedoes which are wake chasers must be considered. And satellite detection of pronounced infrared scars becomes increasingly likely. “Cool” torpedoes may be at a premium for war usage. Considerable work is being done to produce thermal torpedoes with exhaust gases which are soluble in water to reduce wakes and thermal scars. Efforts are also being directed to closed cycle thermal engines which virtually eliminate wakes and reduce thermal scars. Just running a torpedo deep through most of its trajectory is a satisfactory solution for deep water environments. But so much of antiship operations proved to be in shallow waters during World War II, as illustrated by an examination of patrol reports, that today’s antiship torpedoes must seemingly be designed for shallow water use as well as deep water use.
Quite obviously the 29-knot •electric” of World War II was too slow a weapon to fire against high speed warships. But the electrics of today of up to 45 knots speed, have the necessary speed for use against the highest speed warships while maintaining their “stealth” characteristics. Rear Admiral Heaslip, the Head of British Submarine Forces, has stated that his TIGERFISH torpedo, a high speed “electrio”, is his “stealth” weapon for submarine attacks on surface ships. And it is this weapon which is being proposed for consideration in the present competition for a u.s. low-cost antiship torpedo. Importantly, a “stealth” weapon by reducing the amount of warning which it gives to a target in its attack, makes it difficult for the target or its escorts to counter the weapon through evasion or countermeasures. And this element of surprise may be more important today than it was in World War II where Mk 14s got hits despite their wakes having been sighted early in their trajectories.
This has not been an attempt to provide a case for one type of torpedo versus another, particularly since the thermal and electric torpedoes of today have little resemblance to those of WW II. But it does seem that the submarine experience of WW II needs to be recalled to keep present-day comparisons in a proper perspective. The stakes are too high in choosing the best kind of antiship torpedo to not take cognizance of general principles involved in torpedo usage.