The price of speed at sea

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The U.S.Navy's requirement for its new gold-plated frigates* has puzzled many observers. These ships can run at nice sea states with about 44-47 kts, that's up to 18 kts more than some established frigate designs.

You cannot run away from aircraft (including helicopters) or missiles with a ship, and running away from other ships is quite moot because weapon and sensors range and effectiveness de-valued this old concept a lot. Even a 29 kts frigate with relatively modest engines can run away from conventional subs in most sea states, and it's unlikely that running at high speed for long distances is a tactically practical approach for nuclear subs (the Soviets gave this idea up decades ago). The one remaining mystery is whether a ~45 kts top speed (in lenient sea states) helps enough against torpedoes to justify the expense. Torpedoes run -according to public info- at a cruise speed of about 30 kts (maybe a bit less) and sprint during the terminal approach at much, much higher speeds than even a LCS of fast attack craft would be capable (even a hydrofoil design such as the decommissioned Pegasus crafts). Torpedoes are supposed to not be detected (thanks to modestly small and silent cruise) until they're really close, so even the torpedo threat doesn't lift the mystery from the LCS speed requirement.

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Naval engineers can go to great lengths explaining how the huge engines and the high speed-optimised hulls require huge and unusual expenses and compromises. Their talk about shapes and stuff can be boring, though. I decided to show a historical comparison instead:

This is the Japanese small cruiser Chiyoda (1891)**. Nowadays a ship of its size (about 2,500 tons) would be considered a corvette or a very small frigate.

This is the U.S. destroyer USS Fletcher (1942). Nowadays a ship of its size ... oh, wait. About the same size as Chiyoda (2,100 tons).

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The Fletcher uses vastly more efficient oil-fuelled boilers and steam turbines than the Chiyoda with its coal-fuelled locomotive boilers and vertical triple expansion engines. The Fletcher also carries the burden of some electrical equipment (Sonar, Radar).

This doesn't really dampen the effect that I suppose a comparison of both ships' armament has on readers:

USS Fletcher 1942:
5 x 5 in L/38 caliber DP guns
4 x 1.1 inch (28 mm)/75 guns
6 x Oerlikon 20 mm autocannons (very light mounts)
10 x 21 in torpedo tubes
6 x depth charge throwers
2 x depth charge racks
So basically 5 medium velocity 5" guns and ten normal torpedo tubes.

HJMS Chiyoda 1891:
10 x QF 6 inch L/40 naval guns
14 x QF 3 pounder Hotchkiss guns
3 x 11-mm, 10-barrel Nordenfelt early machineguns
3 x 356 mm (14.0 in) torpedo tubes

Twice the gun armament, and a heavier calibre with longer barrels. Three what we would today call lightweight torpedo tubes.

The Fletcher's torpedo armament was about the equivalent of two more 5" guns in weight and weight distribution terms, so a ship half a century later was still much more lightly armed. The Chiyoda equipped with 1930s guns of same weight and size as its 6" guns would have outgunned the Fletchers by a large margin. This was possible despite 50 years of naval technology advance.

Well, what made this possible?

Basically, this was mostly about speed requirements. Chiyoda ran 19 kts (OK for its time), Fletcher 36 kts. Power requirements grow exponentially with speed, so every single knot added to a ship's speed over about 15 kts hurts a lot. A LOT.

Chiyoda had a length/beam ratio of 7.4, whereas Fletcher needed a ratio of 9.4 for its speed. Installed power was about 5,700 to 60,000 hp respectively.

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Chiyoda was a respectable light cruiser in terms of its main guns and their calibre (not quality, of course) by '42. Respectable light cruisers of that time usually weighed about 7,000 to 11,000 tons.

There may be some obscure, brilliant operational research behind the LCS' speed, probably about torpedo terminal manoeuvres. It would surprise since apparently no other navy came to such a conclusion, though.

The more likely explanation for the LCS' speed is that the naval bureaucracy got crazy and irrational, probably trying to sell the ships as sexy and 'never seen before' capable to the taxpayer - and top speed was an easily communicated characteristic.

We already know that the extremely lean crew concept is a failure; working weeks in excess of 70 hrs are exhausting the crews on the LCS prototypes even more than other lean manning attempts did on other USN ships. So we know the naval bureaucracy is not beyond doubt in its attempts at innovation.

In short: The LCS looks like a failure to me. 

Then again, the colonial patrol cruiser F125, the mechanics training ships K130, the shipyard subsidy program known as EGV are horrible failures as well.

S Ortmann

*: Officially known as "littoral combat ship", because "littoral" was en vogue and despite it not being useful in combat for want of punch.

**: Or "protected cruiser". "small cruiser" points more at the mission, while "protected cruiser" is about the construction. Protected cruisers necessarily used coal as fuel, for they used coal as part of their protective scheme. Coal storage at the sides was meant to serve as buffer, where most smaller grenades can explode without doing much harm (combat ranges were short, so only vertical armour was of relevance, deck armour against grenade impact only became relevant in harbour sieges or after about 1900). The other type of cruiser was the armoured cruiser; it used relatively thick belt armour at the waterline to protect its boiler and engine rooms from grenade-caused flooding.

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