Proton is a tanking plane. Same as other supporting units, it does not have any weapons. It is even not armoured. It has two engines similar to the heavy-weight bombers Saturns.
These machines were not constructed to be engaged to direct militant missions. Therefore their resistance is rather low and unables the break Protons through the flak defence of enemy. In the air duels it has to, same as Saturns and Caesars, rely on the support of its colleagues interceptors. The engagement of these machines to bigger air battles is supposed only in cases, that superiority in number of enemy is too big.
Although Protons are existing already for a long time and are used by common army, they have became a part of Signus units armament only recently – because of their vulnerability.