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Lockheed AC-130 gunship is a heavily armed ground-attack aircraft variant of the C-130 Hercules transporter. The plane is manufactured by Lockheed and converted by Boeing. AC-130 in flight releasing flares Why are most of the guns in AC-130 installed on the left-hand side (but not right)?

Picture Source

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    $\begingroup$ Weapons on the other side would be useless because they'd be firing at the sky $\endgroup$ – slebetman Sep 29 '15 at 9:07
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    $\begingroup$ @slebetman I think the question is not only why are there weapons on one side only but also why are they on the left and not on the right. $\endgroup$ – Manu H Sep 29 '15 at 12:37
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    $\begingroup$ The picture above is somewhat misleading. In that image, it is not firing weapons at all. Those are countermeasures. "Most" of the guns on an AC-130 are not on one side, all of them are. $\endgroup$ – T.J.L. Sep 29 '15 at 12:54
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    $\begingroup$ He is talking about the guns not about countermeasures. $\endgroup$ – ACV Sep 29 '15 at 17:16
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    $\begingroup$ I rather doubt there's an extremely good reason for the weapons to be on the left instead of right. They had to pick a side, might as well be the side the pilot sees out of. As a counter-question, why should they not be on the left? $\endgroup$ – MichaelS Sep 30 '15 at 3:43
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It is not designed to strafe, it is designed to loiter over a target or, to apply suppression fire or support fire for a sustained period of time.

It often circles a target area and a counter clockwise orbit (circling to the left) makes sense since the captain sits on the left and can keep the area in view at all times.

Therefore, the weapons are mounted on the left.

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    $\begingroup$ Furthermore, if you've got guns on both sides, it implies that you have enemies on both sides. That doesn't happen very often, so most of the time you're carrying guns you can't use. You could fly back and forth, but then each set of guns is only in use half of the time, while the other set is useless weight. Putting all the guns on one side means that if one of them can see the target area, they all can, so you can use all the guns, all the time. $\endgroup$ – anaximander Sep 29 '15 at 12:10
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    $\begingroup$ A photograph of its predecessor (AC 47) showing this - upload.wikimedia.org/wikipedia/commons/a/a4/… $\endgroup$ – user2896 Sep 29 '15 at 12:19
  • $\begingroup$ Given your answer, I understand that to efficiently pilot this aircraft, you should seat at the left. Does this mean only the captain can do so? $\endgroup$ – Manu H Sep 29 '15 at 12:41
  • $\begingroup$ While piloting the aircraft in normal flight, it follows all the same rules and procedures as any similar aircraft would. When conducting a fire mission, the required pylon turn is probably easier from the left seat, but not impossible from the right. $\endgroup$ – T.J.L. Sep 29 '15 at 12:56
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    $\begingroup$ @ManuH, while that should probably be its own question, I would assume that while the aircraft is circling an unfriendly zone, laying down heavy suppression fire, it's highly likely that the captain would be the PF. Were something to happen to the captain, I'm sure the FO could take over and continue to circle from the right-hand seat, however, they would then have to weight the value of the mission vs addressing whatever issue has caused the captain to relinquish control. $\endgroup$ – FreeMan Sep 29 '15 at 12:56
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Traditionally, the doors most used on an aircraft (including civilian ones) are on the left (captain's) side. Often weapons are mounted in door apertures so that additional holes do not have to be introduced into the fuselage. It follows that there are more, more accessible, pre-existing holes on that side of the fuselage.

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The AC-130 is the evolution of modified C-47s from the Vietnam War. At the time, a small group of USAF personnel explored arming cargo aircraft with side mounted weapons in order to bring greater firepower to bear for ground support. In particular, they wanted to solve the problem of strafing, where aircraft can only bring their firepower to bear for a short period of time, and often without a great deal of time to aim.

Captain Ron Terry was in charge of the initial effort which adapted these planes to gunship use in Vietnam in 1964:

Terry arrived at Bien Hoa Air Base near Saigon on December l. After the miniguns arrived the following week, he selected two test crews of six flight members and an interpreter, and two C-47s with relatively low flight time from the 1st Air Commando Squadron. The planes were modified to accept three minigun pods along the port side (two in the last two windows and one in the cargo door); an MK 20 Mod 4 gunsight mounted in the left cockpit window; and a selective trigger placed on the pilot’s control to fire one or all the guns.

source

Since AC-130s are now specially converted from C-130s by Boeing, and they use modern targeting sensors (IR and visual cameras), and that windows/doors are no longer large enough for the custom mounts they use to install the weapons, there's probably no specific reason for keeping them on the left except that it's the status quo.

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    $\begingroup$ So according to this, the guns were on the left originally because that's where the cargo door was, making it easier to install the guns? $\endgroup$ – fooot Dec 7 '16 at 18:04
  • $\begingroup$ I think it leans that way, I wasn't able to find any definitive source for the technical decisions they made. $\endgroup$ – ww602 Dec 7 '16 at 21:14
  • $\begingroup$ They're on the left because the pilot has to see the aim point. The 'solution' to the strafing problem is to do a turn about the target. By doing that your aim point is the target (no lead required.) The AC-130 has a side-looking HUD for the pilot to see the target and adjust his turn rate to keep it at the center of the turn. $\endgroup$ – Gerry Dec 8 '16 at 13:22
  • $\begingroup$ That's obviously the other option, but I don't think it's definitive. For instance, if you look at the same source I quote above, Capt. Terry says his aiming point is between the left prop hub and engine cowl. My understanding of the site lines of the interior of a DC-7 is that the copilot would be able to see a similar position, so I don't think that was a deciding reason for making that choice. $\endgroup$ – ww602 Dec 9 '16 at 4:08
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All the guns are on the left side. The method of targeting is that the aircraft circles counterclockwise so that the left side is pointing downward. Thus all the guns can be brought to bear on the target (unlike an old frigate with guns on both sides) and the pilot can see the target as he circles.

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    $\begingroup$ Thanks for answering, however, I don't think your answer really added anything to the discussion that hadn't already been stated. $\endgroup$ – FreeMan Jul 6 '16 at 13:31

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