"These soldiers are excellent marksmen equipped with the deadly Bombenschuss carbine. They are equipped with a visor that allows them to hit targets over great distances."
The Marksmen serve as the snipers of the Nazi ground forces encountered in Castle Wolfenstein. They are typically equipped with Bombenschuss marksman rifles and, due to their roles, are lightly armored and have very little health. Often choosing to hang back and lay down suppressing fire, Marksmen are capable of taking off a huge chunk of Blazkowicz's health in very short order, and as such are often prioritized over other enemy types when spotted in the field.
Despite their name, they are seemingly terrible shots, missing the player several times at even medium range. This is made up for by their rifles' high power compared to the Assault Rifle 46-T.
Strategy
The Marksman's behavior is predictable and limited: one will always seek out a piece of cover to hide behind, even if it means charging headlong into the player's line of fire. When they do stop to use their rifles, they will always pause for a short while before actually firing and a glint probably from their visor can be seen, giving Blazkowicz a short window of time to take them out first.
Marksmen are very squishy and thus are usually not worth wasting precious ammunition on. A short volley of bullets from either the Handgun 1946 or Assault Rifle 46-T is usually enough to kill one. When engaged at long ranges they are also highly vulnerable towards their own Bombenschusses, as a single bodyshot will kill them in most cases.
Remaining light on one's feet can help throwing off their aim on lower difficulties. On higher settings it is recommended to find and hug a piece of cover until they are dealt with, however.
Marksmen are hardly ever encountered alone. Stay in cover and keep firing, do not let your guard down untill there are no more bullet tracers to be seen.
Trivia
Rather curiously, none of the Marksmen encountered in the game use scopes, their Bombenschuss rifles are always scopeless when dropped. The reason for this is given as a handwave in their in-game description as them being equipped with a type of advanced visor that magnifies their vision at longer ranges. Such is not a proper setup for a sniper, as their optics are not zeroed to the rifles they carry however magnified they might be, and as a result would not offer much tactical usefulness in a realistic situation. Still, in the character menu in the picture above, the rifle has a scope.
Oddly enough, Marksmen never turn into Shamblers when killed, nor is there any infected/undead version of them found in the game. In fact, they are absent entirely from gameplay upon the player encountering their first Shambler until the final chapter.
Their visor face mask device is similar to the real life THALES LUCIE, a compact generation 2 night vision goggle introduced in the 1996. The LUCIE is unique in that it is a flat appearance with a "folded" light pathway, with the objective lens in the upper corner and the actual eyepiece in the lower back half of the device and the image intensifier at an angle in the housing connecting the two.
Sniper has other meanings. See Sniper (disambiguation) for other uses. 
