This perk makes targeted enemy vehicles within 10 degrees of your reticle remain visible for two more seconds than they normally would be. Your crew will only make use of this perk while in arcade view or sniper view. Your crew will not make use of it while in strategic view (SPG only). However, any vehicle will benefit from a team mate's use of this perk, including SPGs using strategic view. If two Gunners have the perk, the effect is not cumulative.
However I am fairly sure that was the original description, because in-game it says something totally different:
I retrained my artillery gunners to have this skill a while ago because it explicitly said it works in SPG view, but now I am questioning myself again...anyone have a link to a dev comment clarifying this?