That's definitely an improvement, but the torp should remain at top speed even if it is pre-enabled. Once it is enabled, it is almost certain that it will be detected and that the target will commence evasion. Or more likely, the player will enable the weapon precisely because it has been detected and time is of the essence. The fact that the weapon snakes while it is enabled takes away from the benefit of increasing its speed.
Maybe I should take a step back conceptually. Remember when 1.04 was first released and a few people were bitching about how the Mk48 had reduced range at maximum speed, and that targets were often outrunning the torpedo? I discussed the concept of "no-escape range," the range that the torpedo had to be fired from in order to ensure that it could not be defeated by dragging alone. In my view, a mod such as yours increases the probability of a successful kill by effectively increasing the no-escape range by making the weapon harder to detect until it gets close to the target--it decreases the time the target has to run. Once the weapon is detected, though, the benefit of the mod is at an end; at that point, the most important factor for a successful intercept is a high closure speed. The best closure speed occurs when the torpedo is at maximum speed and is on a lead pursuit intercept course. If the weapon goes back to pre-enable speed or is snaking, the closure speed is reduced substantially, giving the target more time to get away. Snaking and reduced speed (if below max speed -10kts) also decreases the linear range of the weapon, so the target needs less time to get away too.
In most situations, the shooter would be better off presetting to max speed. The only situation in which the shooter would be receiving a benefit from having max speed available only after enabling would be in those cases where acquisition occurs immediately upon enabling. I should certainly hope that those instances are rare, except when attacking the most deaf of targets (keeping in mind that reducing the speed of the torpedo below maximum -10kts carries a range penalty, so super-low speed torpedoes will not be employed as a practical matter).
As a suggestion for improvement, I'd recommend taking a look at the LW/Ami 4 torepdo control doctrines. That system demonstrates how you can use the interface to allow the user to control the speed and depth of the torpedo. If you modified that system to allow for the torp to return to preset speed upon command (assuming it needs such a feature), it should be possible in the same way changing the depth to the preset level is possible. One might also be able to have fixed speed settings that are always available regardless of presets, like the UUV controls. Combine this sort of interface with an improved sound-speed curve, and then you've got a great torpedo mod.
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