I work for the Tank Automotive command and have performed as a welding specialist Quality Assurance with armor materials. It is not a big secret like others have mention for welding armored plate. We dont have welders locked in a secret room to perform welding. The material technology is sensative and the accoutability of some material is more closley controled through security procedures than other materials which can be purchased comercially. Watch the armor shows on discovery about the M1 Abrams Tank. I worked on the tank probgram for about 6 years to include production QA, shipment and maintenance. If you would like to learn more about Armor material you could look at clasified army web sites. Do your standard google search word search "armor steel armor plate" etc and you will learn more. Also go dirrectly to the materials manufactureres webs sites for additional information. In the past, U.S Army had special requirements for material and welding procedures for PQR and weldor qualifications. 20 years ago I came to the government as a AWS CWI from private industry and was surprised that we (the army) developed a welding spec for just about every vehicle we had with special testing for armor welding. It seemed ridiculous to me that the army was way behind industry for standarizing specifications. Now we have deleted just about every armor welding specification, replaced with standard industry specifications. I wrote (17 years ago) a standard clause for welding requirements. Guess what I used as a reference, you guessed it AWS. One secret "industry developed technology" is and always will be the best standard for welding. Fabrication of ARMORED TANKS have nothing different than what industry has not already used for years. We have the same welders for tanks that other have for structual buildings. The difference is the controls we put on procedure and welder qualification along with material certification. In AWS there is prequalified joint welding procedures that do not require testing prior to use. To document and understand what are the essential variables used to qualify a procedure during test is what you should focus on. When you weld high carbon steels (like armor) you use high tensile electrodes and higher preheat / interpass temperatures. Just like the AWS preheat and electrode selection tables. The skill level required for welding armor is no less than non armored materials. The only difference is We will not tollerate poor qualification/qualify controls for the welding process. Learn about performing a market survey for welding armor and you will find see what I say is true. Hope this helps
Dominic