Today, the work that tactical officers need to accomplish is no less difficult and life threatening than some of the most advanced military teams. And officers are legally responsible for all of the actions they will take. Each officer has a specific role within a team and must train for his specific job function to make that team stronger as a whole. Tactical entry work is the most physically demanding task an officer will ever be asked to perform. In carrying a ballistic shield, an officer should exercise specific body parts to make himself more mobile and lessen fatigue while carrying it over an extended period of time. Primary engagement officers, the first through a door or the first after the bunker man, need to be some of the strongest on the team. They need to rapidly physically control offenders and hostages, and fend off those who are in the way. These assaulters need a good balance of upper body arm and leg strength. Breachers are usually the first to the door but the last in. If the breacher is inadequate to the task at hand any tactical operation that occurs is doomed to failure. The officer assigned to these responsibilities should train according to the same pattern as the other assaulters, but must also pay attention to the development of the upper body, legs, and pelvic region. Countersnipers are the most dependent of all tactical officers on cardiovascular fitness to low crawl, climb, run or hike into position in order to perform their tactical function. All officers within the unit must achieve a significant level of cardiovascular fitness in order to train their hearts and lungs to provide enough oxygenated blood to the body.