Is there a word for making a weapons system (a rocket, a tank) inoperable when placed on public display, e.g. in a museum?
What comes to mind is defuse (this seems limited to bombs), disarm (perhaps OK, but I associate "disarmament" with a large scale political process), demilitarize (I think this applies more to territory).
Terminology will depend on the weapon. A rifle might be plugged, usually by installing a plug in the barrel or chamber. Something larger, like a tank or a warship, might be decommissioned or, colloquially, mothballed (from the practice of preserving woolen clothing with paradichlorobenzene pellets.)
Cannon may be converted into quakers, non-firing replicas named for the pacifist Society of Friends. Quakers originated as deceptive strategy, intended to make an enemy think that a fortification was armed when it really wasn't.
See this article from The History Channel for some digressively interesting background.
Deactivation is the legal term in the UK which is applied to the approved methods that can be used to render a firearm inert in a way that prevents it being converted back into a live firing weapon. You even get a certificate to go with your deactivated firearm. If it's a tank or something similar, the term is only applied to the gun in it, not the whole vehicle.
Rendering something inert is a more general term for making a weapon (including things like grenades) harmless. I'm not sure if that could be applied to a vehicle or aircraft though, I think decommissioning is a more appropriate term for a vehicle.
"Safing" covers a lot of territory. I would say "safing for display" to distinguish that from safing-for-transport or safing-for-maintenance. It may be more appropriate for some weapons than others. In the missile business, we installed safing plugs into electrical sockets.
Safing:
As applied to weapons and ammunition, the changing from a state of readiness for initiation to a safe condition. Also called de-arming.
note above: de-arming, not dis-arming.
With respect to explosives themselves, Render Safe Procedures (RSP) is the catchall and the acronym is used as a verb as well as a noun. You're going to hate this example.
The responsibility of the bomb squad is to RSP improvised explosive devices ...
https://www.brennancenter.org/sites/default/files/analysis/Miami%20PD%20SOP%202.pdf
Disabled weapons is a catch-all term used here in the UK. Unfortunately as a pair of words it's more common in other senses but a search for '"disabled weapons" legal' will return hits such as this Australian example.
Unlike safing a weapon, disabling it is intended to be permanent, though reactivated weapons are a notable source of funds for criminals. As this suggests, deactivate is used similarly to disable.
You might think this word applied only to territory, but
demilitarize
does in fact appear to be the word that the Department of Defense of the United States uses for this purpose. From a presentation by the US Defense Logistics Agency:
To Demilitarize or DEMIL a piece of property means to remove its offensive and defensive capabilities.
From US Army Regulation 700-144:
Demilitarization
The act of destroying the military offensive or defensive advantages inherent in certain types of equipment or material. The term includes mutilation, dumping at sea, scrapping, melting, burning, or alteration designed to prevent the further use of this equipment and material for its originally intended military or lethal purpose regardless of the condition of the item. Requires total destruction of the item and components so as to preclude its restoration or repair to a usable condition.
In practice, "total destruction" (mentioned in the final sentence of the definition) seems to mean merely that it is not practically possible to restore the item to working condition.
Consider,
incapacitate
To make unable or unfit; esp., to make incapable of normal activity; disable. YourDictionary
neutralize
To render safe mines, bombs, missiles, and boobytraps. Dictionary of Military and Associated Terms
"Deactivated" is probably the most technically correct single word answer, but in North America at least, the noun "DEWAT" or "Dewat" is sometimes used also as a verb.
Eg: "That rifle has been deactivated; it is a DEWAT."
is correct usage, but it would also be common to hear something like:
"She had the rifle dewatted because it would be illegal to have a functional one in her collection."
Here is a definition from the BATF in the US:
10.1.5 DEWATS. Deactivated War Trophy (DEWAT) firearms are still firearms under the NFA, >but have been rendered unserviceable (i.e., incapable of discharging a shot >by means of an explosive and incapable of being readily restored to a >firing condition). The deactivation may have been accomplished by various >means such as (but not limited to) welding of the chamber, cutting the >barrel/chamber/breech, plugging the barrel, welding the bolt to the >chamber, or some combination of these actions which rendered the firearm >incapable of firing a shot.
(https://www.atf.gov/file/58166/download)
It can also be applied to things like artillery pieces and shells; for instance: http://laststandonzombieisland.com/2014/10/05/want-a-dewatted-bofors-just-25k/.
The closest I can think is spiking a gun.
Initially the term was used for sabotaging a gun barrel so it can't be easily used by an enemy. It still generally looks the same on the outside, but it can't be actually used to fire without a lot of work removing the spike.
Displayed military hardware typically has a more thorough version of the same operation done to it (eg: Pouring concrete down the barrel), but I've heard the term used in that context. This can also be referred to as "Plugging" the gun (hat tip to @Hot Licks for this)
I agree with disarmed.
Random House says that disarm means "to remove the fuse or other actuating device from something (e.g. a bomb)".
An arm is "a means of offense or defense; weapon". So to disarm something is to render it a non-weapon. It works for me.
Demilitarize is the proper, "professional" term.
