I am currently working on a project to autonomously navigate a manned submarine through a course in a test tank 50' wide x 1/2 mi. long x 22' deep. For the most part, the sub has neutral buoyancy and just needs to navigate a straight line, however, we would still like to monitor the 3rd axis. The problem is that the speed is about 7-8kn. Our calculations are showing that there may be a situation where there can be a sideways drift undetectable by the accelerometers if we do not have a Gyro in the system. If this is the case, at that speed a crash is surly eminent and could be disastrous. Does anyone have any experience that may guide us in this situation? We are also looking at sonar, but we believe the tank may be too small, causing too much noise to be able to adjust for sufficient accurate sensitivity. Our budget for this control is going to be approximately $4000. Thanks in advance...