The Tesla cannon is a pre-War designed shoulder-mounted heavy directed energy weapon, designed to replace conventional anti-tank weapons. Based on Nikola Tesla's designs, the weapon entered limited production before the war and remains a rare sight in the wasteland. However, it remains a powerful tool in the hands of a skilled user, as the focused energy blast will not only deliver massive damage to the target, but the nature of the blast will also deliver a potent electric shock.
The modified Tesla canon employed by Lyons' Brotherhood of Steel is far more powerful than the pre-war Tesla canon. Discharging a large electrical impulse upon impact with a much larger area of effect. This explosive damage makes the Lyon's model far more suitable for anti-Vertibird use.
The Tesla cannon is a shoulder-mounted energy weapon that fires powerful blasts of focused blue electricity, powered by electron charge packs. The blast is powerful enough to short the electrical circuitry in Vertibirds and destroy them instantly. When fired at enemies, a cloud of residual electricity that damages them for a few seconds.
If you blew up the Citadel, you can find 2 Tesla cannons in the Citadel armory. If you did not blow up the Citadel you can pick the lock to get into the armory but there are no Tesla cannons there.
If you return to Adams Air Force Base after Who Dares Wins, you can acquire 8 more Tesla cannons (4 in perfect condition, 4 in poor condition).
The first pair are before you reach the hangars. Traveling northeast from the Adams Air Force Base Entrance towards the hangars, the 4th open-topped military truck in your path has a resupply crate in the back with a good and poor condition weapon and electron charge packs.
The second pair of cannons (along with some electron charge packs) is in a resupply crate between the first and second hangar on the way toward the Mobile Base Crawler by the base of an Enclave barricade. To be clear, these two hangars are to your right once you reach the airfield portion of your base, near 2 parked Vertibirds.
The third pair are in a resupply crate by the ramp leading to the covered catwalk between the second and third hangar on the way to the Mobile Base Crawler.
The fourth pair are at the base of an Enclave barricade, between the Mobile Base Crawler and the Air Control Tower. The Crate is inside the ring of Sandbags underneath a Brotherhood of Steel Paladin.
It is also possible to obtain an unlimited amount of Tesla cannons from Adams Air Force Base. This can only be done before you destroy the Mobile Base Crawler. Simply observe the battle between the Brotherhood of Steel and the Enclave and at some point a paladin will bring out a Tesla cannon. Go around the force field and loot his body when he dies, then go back and wait for another. Note that the other Brotherhood of Steel soldiers may loot him before you get there leaving you to only get armor or ammunition.
The Tesla cannon has a "shocking effect" much like Jingwei's Shocksword. After hitting an enemy with a blast from the cannon, they'll be surrounded by an electrical effect for a few seconds which will cause damage.
The Tesla cannon has a splash effect when the projectile strikes any hard surface, damaging all near impact. It is entirely possible and quite common for this weapon to strike multiple enemies. Be aware, though, that this effect will also harm yourself or any companion.
If you look into the barrel, you can clearly see the Tesla coil, which is its main component.
Star Paladin Cross and Clover will equip the Tesla cannon when given with ammunition, however, please note that when the cannon is placed in their inventory along with ammunition, it will degrade as normal. By stunning her with Paralyzing Palm, Sydney will equip the Tesla cannon when given with ammunition and it will not degrade.
When in V.A.T.S., if you use two shots, and the first shot doesn't kill an enemy, but the shocking effect does, you will still fire it again even though the enemy is already dead.
If you have the Grim Reaper's Sprint perk, this weapon may not always refill your AP after killing someone in V.A.T.S. This happens due to the aftershock effect.
Interestingly enough, this weapon's laser, or rather its aftershock effect, passes through walls and other solid barriers (i.e. you can shoot the Citadel Laboratory wall next to the map and Rothchild may be knocked unconscious).
The Tesla cannon has a script effect attached to it that allows it to destroy airborne Vertibirds with a single shot, regardless of actual damage done.
The Tesla cannon tends to kill a stronger enemy (Enclave Hellfire trooper for instance) in 1-2 shots (1 with aftershock). Also note that the after shock can harm the player and followers in close ranges. Try to aim for the enemy in the middle as the after shock will soften up the enemies around it, then a more practical firearm can be used if desired.
A Tesla cannon was first planned for inclusion in Fallout: Brotherhood of Steel 2, as a "high-powered mass-cannon throwing tessellated plasma forward in an orgy of death and destruction", assembled from parts found during the game (including a Tesla coil).
Xbox 360PC If you kill an enemy with the splash damage effect alone, you may not earn XP for the kill, but you can use this to your advantage. If a good character is killed by the shock damage after effects it will result in no karma loss or hostility from nearby non-player character's. You will also not receive any fingers or ears for enemies killed by the cannon's splash damage.
Xbox 360 Occasionally while in third person the Tesla cannon will float off of your back and stay suspended in mid air. This makes it impossible to use in third person and V.A.T.S., however the Tesla cannon will still work in first person. (This will fix itself after a while however there is nothing that you can do to fix it)
PC The Tesla cannon will not destroy a VB-02 Vertibird in a single shot, unlike the console versions of the game.