In a message forwarded by Charlie Spiegel: I can’t seem to locate the trajectories (cruise vs. ballistic) in Annex D. They seem to be listed for Aircraft ordnance in Annex G4 (I think) but the data for ship weapons is nowhere to be found. Am I missing something? My answer: You’re right. They’re never explicitly described. A cruise missile is easy. After launch, it holds the same altitude over its entire flight path. Many surface-launched missiles, even if they are sea-skimmers, will climb to Low altitude the turn of launch, and many antiship cruise missiles will change altitude as they approach the target. These special maneuvers will be mentioned in the remarks for that missile. Ballistic missiles, or more properly, “missiles with a ballistic trajectory,” are harder. They follow an arc from launcher to target. Most of the time the exact altitude can be ignored, but if the missile might be engaged by some weapon with a limited envelope, its exact altitude may matter a great deal. If the launcher is higher than the target (air-to-surface), the missile descends. Ideally, the shooter should divide the time of flight in turns by the number of altitude bands the weapon must descend (don’t count VLow as a separate band), then step the altitude appropriately. In practice, the missile usually only has to descend two or three levels, so it’s easy to figure out when the missile will change altitude. Missiles lower than the target will climb, dividing their time of flight equally between the levels that divide them from their target. Missiles launched from the same altitude will arc up one level higher and then arch back down, so their time of flight is divided into thirds, with the middle third at the higher altitude. Figuring out the exact altitude level of a missile on a ballistic trajectory can mean a lot of fiddle work. It can be necessary, though. Stephen Lox sent in the following question: When a platform is cavitating or using active sonar what is the effect on its own passive sonar? Remember, it does not take much for Noisy vessels to cavitate. Chris Carlson answers: We ignore cavitation this case, since all that noise is in the baffles of the ship’s hull arrays and the sonar is blocked from looking back there anyway. While technically possible, no Noisy or Loud ship would be fitted with a towed array, so we didn’t include a modifier that just wouldn’t be used. Basically, its the flow noise over the array that matters and that is just a function of speed. As for active sonars, if you are in active mode then you really can’t use the passive mode, since the transducers are putting acoustic energy into the water and then looking for a BT significant echo. This basically requires a different system lineup from the passive mode. From Stephen: How does Harpoon 4 handle what range a sonar can detect an explosion? Chris answers: Treat explosions as a Loud target for purposes of detection range, they are about the same in terms of source level as an active sonar pulse. The only difference is that all sonar frequencies (VLF, LF, LF-MF, MF, and HF) can detect an explosion. Many people have asked about the lack of a height-finding radar on the US O.H. Perry FFG. Chris Carlson provides this explanation: The Mk92 fire control radar performs a height-finding function by spiraling a beam up and down as it searches. Its not the most efficient way to do business, but it does work for the relatively short range of the SM1. BT Back to The Naval Sitrep #20 Table of Contents Back to Naval Sitrep List of Issues Back to MagWeb Master Magazine List © Copyright 2001 by Larry Bond and Clash of Arms. This article appears in MagWeb (Magazine Web) on the Internet World Wide Web. Other military history articles and gaming articles are available at http://www.magweb.com