Technical intelligence (TECHINT) is the discipline of exploiting intact (or largely intact) equipment, supplies, etc. from an actual or potential opponent. It is often, but by no means exclusively, the set of techniques for gaining information from captured materiel. The essence of TECHINT is that it deals with things that are as close to usable as possible. Reverse engineering, the practice of learning how to build something by analyzing a finished example, is a (usually) civilian equivalent.
Comparing the TECHINT approach with those of several complementary intelligence disciplines will put it into perspective. Assume that it has been learned that an enemy has a new artillery rocket. TECHINT staffs, called a Captured Material Exploitation Center (CMEC) in a U.S. joint command, or an appropriate office in the Defense Intelligence Agency, will prepare guidance called "templating" on where the rocket might be found, how it can be recognized, and all that is known about safely handling it.  Assume that a rocket is safely in hand. The TECHINT analysts will examine the rocket, its launcher, and any equipment found with it. They might disassemble it, nondestructively testing the components. As a final step, they could reassemble it, and fire it on an intensively instrumented test range. They want to discover tactically relevant things about it: its range, warhead characteristics, accuracy, susceptibility to electronic warfare, and its characteristic signatures that can be recognized by radar and other field sensors.
During that test firing, measurement and signature intelligence (MASINT) analysts will be using a wide range of techniques to characterize the signature of the rocket's use: its radar reflection; its exhaust plume temperature and composition (i.e., using spectroscopic MASINT); exhaust products at the launch site and captured in midair (i.e., materials MASINT), and many other parameters that come during and after the use of the intact rocket.
On a strategic level, the scientific and technical intelligence (S&TI) community would look less to the operating characteristics of the rocket, and more into what it tells them about the research, development, and manufacturing capabilities of the enemy. If the rocket casing appears to exploit new aerodynamic or stealth characteristics, what does that say about their simulation and computation capabilities? If the casing is made of exotic composite materials, the mere "fact of" their use tells things about their chemical and fabrication technology.
Acquiring the materiel
Goals in obtaining the materiel, or closely associated information in such things as operation & maintenance manuals, are to get things that are as close to new condition as possible, and in a way that subjects one's own forces to the least risk. If the equipment can be legally or illegally bought, that is likely to provide better information than equipment captured by a planned raid on a field facility, and that is likely to provide a better product than one in a position overrun during battle.
Read the fine manual
Even documents, in a language not understood by the field team, can be informative. If, for example, an Arabic-language manual is found in a Spanish-speaking country, even without knowing the full contents of the document, it may indicate that Arabs are training the military force that had the manual. This sort of inference from the document itself, rather than its content, is known as document exploitation. 
Purchase, bribed access, and theft off the battlefield
What has proved to be a series of particularly capable Russian anti-shipping missiles, which had been grouped under the NATO reporting designation SS-N-22 SUNBURN, were the targets of many collection operations during the Cold War. These remain of great interest, since Sovremenny-class destroyers that carry them have been sold to China, and China may be manufacturing copies.
While the deals have changed frequently, U.S. Boeing has had several proposals to buy a SUNBURN variant for development as a target drone.
Well-publicized offers to enemy personnel to defect, bringing key equipment, can have multiple benefits for one's side. It will make the other side extremely aware of a security threat, and, if the security services of that country are strong, their protective measures may interfere with effective operations.
If the offers are accepted, of course, it provides immense value to the TECHINT effort, especially since the equipment usually comes with someone who can explain its use.
PSYOP specifically designed to provide TECHINT occurred during the Vietnam War. A PSYOP campaign encouraged enemy soldiers to surrender with their weapons and equipment intact; rewards were offered and paid to Viet Cong and NVA troops who did this. This type of campaign not only reduced the number of weapons available to the enemy but also provided a continuous source of materiel for the CMEC to exploit.
Operation Moolah: one MiG-15, delivered
On 1 April, 1953, the U.N. Joint Psychological Warfare for the Korean War approved Operation Moolah. Leaflets and radio broadcasts offering a $50,000 payment to any pilot who flew a MiG-15 to a U.N. base, with a bonus of an additional $50,000 for the first pilot to do so.
The offers were made in Korean, Chinese, and Russian, since while all North Korean combat aircraft were marked with North Korean insignia, some of the combat units were homogeneous Chinese and Soviet Air Force organizations. 
Viktor Belenko and the [[MiG-25]
Some defections are purely ideological, as was that of Soviet pilot Viktor Belenko, who flew a MiG-25 to Japan. While the Japanese returned the aircraft — neatly disassembled — Belenko came to the U.S. and consulted on air tactics.
If equipment of interest can be located, especially in an area where it is isolated from combat forces, a raid, by special operations forces, can be mounted to physically remove as much as possible, then measure, photograph, and destroy what cannot be taken.
Operation BITING: German WWII Würzburg radar
The better the understanding of the target, the more productive a "kick down the door" raid can be. British scientific intelligence, under R.V. Jones, had learned, through electronic intelligence and human source intelligence, the principles of a radar known as Freya. Given that information, they looked, in imagery intelligence photographs, for equipment consistent with the their understanding of its electronics, and sent out photographic aircraft to get more detailed pictures, as well as to look for a complementary piece of radar equipment. They knew, from communications intelligence, that the other device was called Würzburg.
As the locations became known, electronic intelligence receivers were directed at them, to learn as much as possible from the signals. At the time, there was a British policy, not long after Dunkirk, to harass the Germans with raids. On balance, the Germans knowing that the British had captured a radar and would know its details were counterbalanced by the fact that the radar was widely deployed and could not easily be changed.
Since the radar itself was too large for raiders to take with them, it was decided that someone with technical knowledge had to be in the raiding party, to remove components that could be removed, and make measurements and photographs of the key components that could not be taken. The most knowledgeable British scientific intelligence officers were not permitted to be put into situations where they could be captured, so a combined approach was developed. As the raid, called Operation BITING, was readied to go against the German installation at Bruneval, France, it was decided to make it a combined paratroop and amphibious operation. A scientist with less detailed knowledge than Jones' immediate staff, D.H. Priest, was allowed to be on one of the naval vessels, and go ashore only if security permitted. For the first wave, a radar technician, C.W.H. Cox, volunteered to go in by parachute, and did the actual disassembly.
Operation Rooster 53
In 1969, the Israeli military became aware of the Egyptian air defense system being enhanced with then-new Soviet SPOON REST long-range search radar. While the first plan had been to destroy it, the recent Israeli acquisition of CH-53 heavy-lift helicopters gave them the option of capturing the equipment and bringing it back, intact, for detailed analysis. 
Field units, in the course of their operations, may encounter unusual equipment, which may be on the template provided to intelligence personnel, or be a total surprise. Especially in a fluid battle situation, where one's own forces may not be able to hold the position, an immediate report should be sent to the intelligence channels. If photographs can be taken, serial numbers written down, exact (GPS) location noted, etc., by the field unit or front-line intelligence personnel, these may be valuable if the equipment cannot be taken back for analysis.
Assuming no immediate enemy threat, the troops that discovered the materiel should secure the area around it, but should not touch it or approach it closely until explosive ordnance disposal specialists have declared it safe to handle. When the UN teams searching Iraq for weapons of mass destruction after the Gulf War showed shells, rockets, etc., to news teams, it was not coincidental that their explosives and boobytrap specialist, Jack McGeorge, was holding the item or was the closest to it.
In addition, valuable information, such as operating frequencies, may not have been cleared from communications-electronics equipment. Components of such equipment also may, even if the equipment appears to be powered off, still hold hazardous electrical power. "WARNING Components, control knobs, and switches on C-E equipment MUST NOT be touched until the equipment is photographed or positions recorded by TECHINT or other trained personnel to avoid the possibility of immediate personal injury or damage to equipment"
One of the reasons that combat capture may be the worst way to acquire equipment is that the enemy that possessed it may have followed orders to remove or destroy critical components, or set controls to misleading value. On a battlefield, the enemy has ready access to explosives or weapons fire for destroying it, or very straightforward means such as driving over it with a tank. They may have specific procedures for destroying the components in order of criticality. 
Much TECHINT analysis, of course, will be specific to the type of materiel found. As in combined arms warfare, some of the analysis will be interdisciplinary. For example, communications engineers will be the first to analyze radios found at an artillery fire base, but, once it is determined that the radios are used in fire control, gunnery specialists will need to become involved to understand both human and direct equipment interfaces.
Medical intelligence is often considered a subset of TECHINT, and, of course, will require appropriate health sciences professionals to analyze the use of medical equipment. The medical intelligence mission goes beyond captured equipment, to evaluate such things as environmental hazards and endemic diseases in a particular areas.
When guided missiles are to be examined, the appropriate specialists will be needed, since, after all, that is rocket science.
U.S. Army doctrine can put seven kinds of classic TECHINT analysts in a field team, all dealing with the direct function of equipment and materiel. In addition, MASINT specialists look at the indirect signatures of the equipment and materiel. The disciplines are: communications-electronics, automation systems, weapons, munitions, WMD, medical, mobility/transportation.
Location found vs. probable source
Weapons designers, or design organizations, often have characteristic styles. If, for example, a piece of anti-aircraft artillery, appearing to be Soviet-designed, bas Chinese markings on parts and shipping tags, several things can be inferred. First, China may be manufacturing a clone of a Soviet design that had previously thought to be Soviet-only. Second, if the side that had the equipment was not known to be a Chinese client, it would then become an intelligence research requirement to see if China was supplying the country, or if the equipment was available on the world arms market. 
Packaging and means of shipping equipment can be quite informative; sometimes detecting characteristic shipping containers or specialized trucks are a strong indication of the presence of equipment not otherwise visible. Roger Hilsman explained that the U.S. had developed an extensive data base of Soviet "crateology", or the shape of packaging for particular weapons. He gave the example of recognizing the movement of an Il-28 bomber as a set of crates on the deck of a cargo ship, as the particular shapes and sizes reflected the standard means of disassembly.  The technique of crateology arguably is imagery intelligence interpretation technique, but, like so many other intelligence discipline, the line blurs between the sensor (i.e., the imagery proper), and whether the analysis is more discipline-specific aviation TECHINT. An example of a representative crateology technique is shown in Photograph 9 of Cuban Missile Crisis photographs..
Technical intelligence training
Technical Intelligence Analyst Course
- Air Land and Sea Applications Center (9 June 2006), TECHINT: Multi-Service Tactics, Techniques, and Procedures for Technical Intelligence Operations, [joint manual] (U.S. Army))FM 2-22.401/(U.S. Navy)NTTP 2-01.4/(U.S. Air Force AFTTP(I) 3-2.63 p. IV-2
- TECHINT, p. D-1
- FM 34-54, p. 5-10
- Friedman, Herbert A., Operation Moolah: the Plot to Steal a MiG-15
- Barron, John (1983), Mig Pilot: The Final Escape of Lt. Belenko, Avon
- Jones, R. V. (1978), The Wizard War: British Scientific Intelligence 1939-1945, Coward, McCann & Geoheganpp.193-201
- Jones, pp. 233-249
- Operation “Rooster”— Israel Captures Egyptian Radar In War of Attrition (December 26-27, 1969), Jewish Virtual Library
- FM 34-54, p. 4-7
- U.S. Department of the Army (12 November 1971), Procedures for the Destruction of Aircraft and Associated Equipment to Prevent Enemy Use
- FM 34-54, p. 3-10
- TECHINT, p. D-1
- Hilsman, Roger (1967). To Move a Nation: The Politics of Foreign Policy in the Administration of John F. Kennedy. Doubleday.
- National Security Archive (2002). The Cuban Missile Crisis 1962: The Photographs. George Washington University National Security Archive.
- Hasenauer, Heike, Foreign Material Intelligence Battalion