1st echelon maint.: You own a computer and you are the operator so you perform first echelon maint on it by keeping it clean and listening for the fan running.
2nd echlon maint.: Usually your unit maint facility. When, in performing the 1st echelon maint discover you can not hear the fans turning, you turn the unit in the 2nd echlon maint facility for repair.
3rd echlon maint.: The guys at the unit level were unable to repair the equipment. The more with the unit and just have common spare parts and a limited amount of test equipment. 3rd echlon maint would usually be at a base or at least in a fixed area where good power could be provided for test equipment and have a large stockpile of parts, common and not so common.
4th echelon maint: Boy, you really screwed up that little computer didn't you? Usually there is only one 4th echelon unit in each military area. I believe there used to be a total of eight in the US. IF the equipment must be sent to 4th echelon, the decision must be made if the equipment is actually worth the maint time. A piece of equipment may be considered a loss and submitted to DRMO rather than be shipped to 4th echelon.
5th Echelon: Actually this is not a military maint facility. This is usually factory maintenance at the orig. manufacturer. This is used in cases such as a helecopter that has been in storage for 10/15 years and now is going to be put back in service. This piece of equipment needs to be gone over, every brace, strut, rivet must be inspected for damage/rust and repaired. When the unit comes out it will be in "like new" condition.
Additionally, if you deal with equipment manuals or have any of them. They in with a dash (-) and then a two digit number. IF this number is -10 then the manual is an operator (1st echelon manual). If it is a -20 then it is a 2nd echelon manual. IF the equipment is small, such as a field phone, manuals may be combined so you will se a number such as -14, this manual covers all maint from operator (1 echelon) through depot (4th echelon).
This post is probably in the "way too much info" category, but I thought a few of you might be interested.