Optimization, suboptimization…

2013/02/07 04:36
jerrypournelle @ Chaos Manor – Jerry Pournelle

http://www.jerrypournelle.com/chaosmanor/?p=11898

…if you couldn’t measure something you couldn’t do much about it. This led to the temptation to study what you could quantify and measure. Often that was a good way to go, but sometimes it led to exactly the opposite result of what you wanted – if you chose to optimize on the wrong objective. This was known in the trade as sub-optimization, and one case of that nearly led to disaster.

In the early days of World War II, the O(perations) R(esearch) boffins were aimed at the problem of the Battle of the Atlantic. England’s survival depended on getting convoys through to the island nation. The Germans rightly believed that England could be blockaded and starved into submission. After all, Britain had done that to France in the Napoleonic wars. Germany had no surface fleet to challenge the British – and later American – fleets, but they did have submarines, and some very effective submarine tactics.

The OR boffins studied the situation and came up with optimum techniques for the escorts to use to sink submarines. In particular the trick was not to attack too early after an air sighting of a surfaces sub. Hang on until you vector an escort ship to the scene then have a coordinate air-sea attack. That gave the best probability for sinking the sub. It worked, too. The number of subs sunk went up. The problem was that the number of cargo ships sunk by the subs went up, too.

The problem was that they had chosen the wrong measure to optimize. After all, the goal was not to sink subs. The real goal was to get cargo ships through the submarine wolf packs.

That, as it turned out, required entirely different tactics. The best tactic to get the convoy through was to attack immediately, and once the enemy sub was submerged forget about it and look for others. Make them stay under water, because by far the most effective attacks were done from the surface, particularly at night. A sub firing a torpedo from the surface had a far higher chance of hitting the target than it did from a submerged release.

And once the boffins figured this out and applied the new strategy, the number of submarines sunk went down and down, but the tonnage of cargo that got through grew. And the battle was won. …