[Neptunus Rex]

On US Subs, the #2 Scope is the Electronic one, with LLTV, OMNI RF Sensor, and in some, limited radio reception/transmission. As the name implies, its all electronic. It's the prefered scope due to the OMNI RF Sensor that lets the operator know that there is radar in use up topside and the scope may be detectable.

The #1 scope (attack) is all optical/mechanical. Pretty much the same type of scope that was used on WWII Fleet boats. Smaller window and mast head width, produces smaller wake. Smaller head window lets in less light, but because the optical train has no LLTV mirrors, etc, it's more usefull under low light conditions when use of the #2 scope LLTV would obscure or washout very small details that the operator needs to see.