Chakra Hammer on February 2, 2008 at 1:00 AM

Actually, I have difficulty defining a 600-foot-long, 14,000+ ton vessel intended primarily for long-range engagement of high-value targets beyond the littoral zones as a “destroyer”. A more appropriate term would be “battleship” or at least “battle cruiser”- the latter being a term the USN has never used, in spite of building what amounted to battle cruisers during World War Two, namely the “large cruiser” U.S.S. Alaska (CB 1) and her sister ship, U.S.S. Guam (CB 2). They were named for what were then U.S. Trust Territories, to distinguish them from cruisers (named for cities) and “true” battleships (named for states). (The third ship in the class, U.S.S. Hawaii, was never completed, and the last three, to have been named Philippines, Puerto Rico, and Samoa, were cancelled.)

Hollowpoint on February 2, 2008 at 3:49 AM

You’re exactly correct. A weapon like this has to be fired at a high angle to the horizontal (usually about 45 degrees or so) to acheieve its maximum range, due to the laws of exterior ballistics. During World War One, the German Army shelled Paris from 78 miles away in the Forest of Compieigne
with a 21-cm (that’s about 8 1/2″ bore) weapon called the Kaiser Wilhelm Geschutze. (Her gun crew simply called her La Parisienne.) It had a barrel about 100 feet in length, took a 250-lb bagged charge of powder, and launched a 750-pound shell at 2800 feet per second for the admirable range of 78 miles. To do it, it fired at an angle of 43 degrees to the level, and the shell as a result spent over three-fourths of its flight trajectory actually outside of 90% of the earth’s atmosphere, reaching a peak altitude of about 36 miles. The flight time was about three minutes, and the crew had to do some fairly hefty mathematics to allow for the 14 miles the Earth rotated on its axis while the shell was “up beyond” most of the air.

Accuracy of the beastie was nothing to rave about, as its normal dispersion at the receiving end was on the order of a mile and a half. (Of course, it was shooting at an entire city, and Paris couldn’t exactly move out of the line of fire.) What finally shut it down was the Allied advance in the spring of 1918 which pushed the German Army out of the area, and the gun out of range of Paris.

To avoid such problems with this weapon, I expect that the railgun’s projectiles will have some sort of course correction capability, such as attitude control jets, and will probably be guided all the way to the target by a military -grade GPS system, backed up by an internal strapdown inertial-guidance platform. The difference being, the GPS would take “steers” from a satellite (which could, theoretically, be “jammed” [ECM'd] if somebody on the target end knew what they were doing), while the inertial system would be totally internal, autonomous, and independent, and be uninterruptible for that reason.

Even without GPS (which could drop the round into the proverbial pickle barrel), the inertial system alone would be good enough to get the round to within about fifty metres of the target at 300 km (200 miles) range, and that’s close enough to make things unpleasant for the intended recipient. Especially when the arriving “incoming mail” can do an excellent impression of a meteor impact, with or without an explosive charge, just based on kinetic energy alone.

(Jon’s Law; Any projectile moving at 3,000 m/s has a kinetic energy “yield” equivalent to its own weight in TNT, also often rendered as “Anything moving at 2 miles per second packs its own weight in BLAM.”)

The Navy’s operational railgun will come very close to this level of energy release. My hat is off to Naval BuOrd. Well Done.

cheers

eon

eon on February 2, 2008 at 9:05 AM