A spotter is a part of a two man elite marksman team. A spotter works with a sniper and will provide the sniper with intelligence and information such as: Distance to target, Windage adjustments, Elevation adjustments, Whether the target is Friendly or Enemy, If they have permission to fire at the desired target
In the British Army Snipers use the L115A1 Long Range Rifle, and the spotter is equipped with the L85A2 Bullpup assault rifle, with an attached 4x SUSAT sight.
In the American Army Snipers use the M40A3 sniper rifle, and the spotter will use either and M4 Assault rifle with and ACOG sight (AdvancedCombatOpticalGunsight), or the M16 Assault rifle with an under barrel grenade launcher also with an ACOG sight.
If the two man team comes under fire they will both "bug out" (withdraw) covering each other by a leapfrog type maneuver.
Snipers hardly ever operate without Spotters. Without spotters the sniper cannot effectively operate to their maximum potential.