An airstrike is a military strike by air forces on either a suspecte or a confirmed enemy ground position, which depending on the selected tactics may or may not be followed up by artillery, armor, or infantry units. An airstrike can also be called upon by infantry or other ground forces to soften up or possibly destroy an enemy position; this tactic is commonly used when ground strikes are ineffective, and can also be used in conjunction with Close Air Support. Airstrikes are commonly delivered from aircraft such as bombers, ground attack aircraft, or strike fighters. Weapons used in an airstrike can range from machine gun bullets, to missiles, and to various types of bombs such as nuclear bombs. They are often used in strategic bombing.