movable tail fins. This is an autopilot. To guide the missile, the system has sensors that check that the fins are positioned as requested. If not, the deviation is sent back to the controller for further adjustment. This is a closed-loop controller. There are three stages in the flight managed by the tracker: 1) an initial phase just after launch; 2) a mid-flight phase that lasts for most of the flight; and 3) a terminal phase in which the tracker selects the most effective point of impact. With guidance algorithms, the autopilot uses data from the seeker and tracker to determine when to transition the missile from one phase of flight to another. Depending on whether the missile is in top attack or direct attack mode, the profile of the flight can change significantly. The top attack mode requires the missile to climb sharply after launch and cruise at high altitude then dive on the top of the target (curveball). In direct attack mode (fastball), the missile cruises at a lower altitude directly at the target. The exact flight path which takes into account the range to the target is calculated by the guidance unit. Training A great familiarity of each control and swift operation needs to be achieved before the unit can be deployed efficiently. American troops are trained on the system at the Infantry School in Fort Benning, Georgia, for two weeks. The soldiers are taught basic care and maintenance, operation and abilities, assembly and disassembly, and the positions it can be fired from. Soldiers are also taught to distinguish between a variety of vehicle types even when only a rough outline is visible. The soldiers must accomplish several timed drills with set standards before being qualified to operate the system in both training and wartime situations. There are also smaller training programs set up on most army bases that instruct soldiers on the proper use of the system. At these courses, the training program might be changed in small ways. This is most commonly only minor requirements left out due to budget, the number of soldiers vs. simulation equipment, and available time and resources. Both types of training courses have required proficiency levels that must be met before the soldier can operate the system in training exercises or wartime missions. Combat history The Javelin was used by the US Army, the US Marine Corps and the Australian