tank. Hard kill systems intercept incoming threats with a projectile(s) of its own, destroying the threat. For example, the Israeli Trophy destroys an incoming rocket or missile with shotgun-like projectiles. The Soviet Drozd, the Russian Arena, the Israeli Trophy and Iron Fist, Polish ERAWA, and the American Quick Kill systems show the potential to dramatically improve protection for tanks against missiles, RPGs and potentially kinetic energy penetrator attacks, but concerns regarding a danger zone for nearby troops remain. Mobility The mobility of a tank is described by its battlefield or tactical mobility, its operational mobility, and its strategic mobility. Tactical mobility can be broken down firstly into agility, describing the tank's acceleration, braking, speed and rate of turn on various terrain, and secondly obstacle clearance: the tank's ability to travel over vertical obstacles like low walls or trenches or through water. Operational mobility is a function of manoeuvre range; but also of size and weight, and the resulting limitations on options for manoeuvre. Strategic mobility is the ability of the tanks of an armed force to arrive in a timely, cost effective, and synchronized fashion. Tactical mobility Tank agility is a function of the weight of the tank due to its inertia while manoeuvring and its ground pressure, the power output of the installed power plant and the tank transmission and track design. In addition, rough terrain effectively limits the tank's speed through the stress it puts on the suspension and the crew. A breakthrough in this area was achieved during World War II when improved suspension systems were developed that allowed better cross-country performance and limited firing on the move. Systems like the earlier Christie or later torsion-bar suspension developed by Ferdinand Porsche dramatically improved the tank's cross-country performance and overall mobility. Tanks are highly mobile and able to travel over most types of terrain due to their continuous tracks and advanced suspension. The tracks disperse the weight of the vehicle over a large area, resulting in less ground pressure. A tank can travel at approximately across flat terrain and up to on roads, but due to the mechanical strain this places on the vehicle and the logistical strain on fuel delivery and tank maintenance, these must be considered "burst" speeds that invite mechanical failure of engine and transmission systems. Consequently, wheeled tank transporters and rail infrastructure is used wherever possible for long-distance tank transport. The limitations of long-range