Thursday, May 19, 2011

Bismarck saga -- German destroyers

Narvik-class German destroyer

Around 11:30 p.m. on May 19 a third German destroyer joined the Bismarck's task force as it got ready to pass through the narrow waters between Denmark and Sweden.

It may be wondered why no destroyers accompanied the Bismarck and Prinz Eugen on their foray. Surely a flotilla of escorts would have been useful.

In fact, however, destroyers were inherently limited in ways that precluded using them on long-range commerce-raiding missions. They were small ships which limited the amount of fuel they could carry -- but being tactically useful required them to move fast, which burned prodigious amounts of fuel. In addition the very rough sea conditions common in the North Atlantic often meant they had to slow down in order to avoid serious damage. In many cases a battleship or cruiser could move through stormy seas faster than a destroyer. Being slowed by rough weather was tolerable when acting as an escort vessel -- the merchant ships were slower anyway and the rough seas affected them as well. Likewise the destroyer's main foe, submarines, was also a small vessel that was slow under water and above water was affected just as badly by rough weather.

Every navy found keeping destroyers fueled up a major challenge, but German destroyers, in particular, were short-legged, being designed for use close to home in the North Sea and Baltic. The Narvik class destroyers such as Z-23 were typical, having a range of just 2,180 nautical miles at a speed of 19 knots. In comparison, standard British destroyers like the J, K & L class or the Tribal class destroyers that harried the Bismarck in its final hours had a range of more than 5,000 nautical miles at a sped of 15 knots. Even so, there were several instances during the Bismarck operation where British destroyer operations were affected by fuel considerations.

This is illustrated in the Avalanche Press Second World War at Sea series game Bismarck where the destroyer Z-23 has just 5 fuel boxes while the tribal-class destroyer Zulu has 6 and the JKL-class DD Javelin has 7 fuel boxes. In SWWAS a box provides enough fuel to travel 24 squares on the operational map -- at 1 square per turn! A square represents 36 nautical miles. If, on the other hand, a destroyer goes at its top speed of 3 it will use half of a box in that one turn and the entire box on the next. The Bismarck has 13 fuel boxes -- enough to travel up to 312 zones at slow speed. The purpose-built commerce raiding pocket battleships such as the Admiral Scheer have 22 fuel boxes, enough for 528 zones and transoceanic range.

As we will see, even larger ships such as cruisers, battleships and aircraft carriers, often had fuel problems.

No, the Bismarck, which had a range of more than 8,000 miles at 19 knots and the Prinz Eugen, 7,000 nautical miles at 20 knots, were on their own once they left waters close to Germany. Even their much longer cruising ranges were insufficient for a war cruise and they relied on access to hidden German tankers to refuel at sea and remain on station long enough to be a threat.

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