ENGINEERS IN A NUT SHELL
There is no difference in capabilities based on the type of engineer with one exception - destroying fortifications.
"All engineer squads and vehicles can construct and repair base facilities." (p 140).
All types of engineers can damage facilities for you ("Bases that have been captured have a chance to have their facilities damaged before the capture takes place. The chance and amount damage done can be increased by the presence of defending engineers." p. 197). See pg. 236 for details.
All types of "Engineers can be used to increase the size of airfields, ports, and fortifications at bases, and they can also be used to repair damage to airfields and ports." (p. 214)
"Combat Engineers can also destroy enemy fortifications during combat." (p 179).
Along the same line, if your engineer is not a combat engineer unit, then its combat capabilities are limited: "Support type squads (support, aviation support, and engineers) will only fire if they are being attacked in close combat by enemy troops." (p. 195).
Which engineer units are "combat engineers" and thus can destroy enemy fortifications?
"Construction Engineers have only the word “Engineer” in the device name. Combat Engineer units have additional nationality and function designations (e.g. IJA Engineer Squad, Soviet Sapper Sqd, Aus Cmbt Eng)." (p. 179).
How can I quickly determine how many "engineer" squads and "engineer" vehicles do I have at a base for construction purposes?
On the base information screen:
"»» Engineers - The number of construction troops available to expand the base . . . ." (p. 206)
"»» Engineer Vehicle - The number of construction vehicles used to help expand the base . . . ." (p. 206)
What the heck is an "engineer vehicle"?
"Each engineering vehicle is the equivalent of five engineering squads for these purposes [i.e., refering to the following purposes: "increase the size of airfields, ports, and fortifications at bases, and they can also be used to repair damage to airfields and ports."]. (p. 214).
Expanding multiple capabilities at once slows down your construction
"Engineering efforts will be split between these three items unless you intentionally instruct the base to discontinue the construction efforts of a particular item." (p 215).
Low supply slows your construction (no supply stops it)
"Construction work consumes supplies, and if a base is low on supplies, construction efforts will slow accordingly. One supply point is consumed every twelve hours for each engineering squad (or equivalent) that is involved in construction operations. It is very important that you realize that construction consumes supplies, as it is often best to discontinue construction (especially expensive construction over the SPS) rather than use up precious supplies." (p 215)
The larger the size and the higher you are above SPS, the longer it takes to complete
"Construction costs to increase an airfield or port by one increase as the current size of the airfield or port increases (i.e. it takes longer to go from a size 6 to size 7 than from a size 5 to a size 6). Once a port or airfield reaches its SPS, the cost of additional construction increases significantly, You should consider halting construction or else risk consuming large quantities of supplies for possibly little benefit. In addition to the normal costs, it takes 10 times longer than normal to increase a current size 0 airfield with a SPS of zero to a size of 1. These size zero locations were very unsuitable for airfields (such as Wau, which was built on the side of a mountain). Fortification construction costs are based on the SPS of the airfield and port in the base, with longer time required for bases with larger potential. Construction costs also increase as the current Fortification Level increases." (p. 215)
Repairing base damage slows down your construction
Repairs automatically come before construction: "The remaining engineers at a base that have not conducted repairs will, if the base has been given the appropriate order, attempt to increase the size of the airfield and port and increase the amount of fortifications protecting the base." (p. 215)
How do I repair base damage with my engineers?
It's automatic and there is a designated order: "Each turn, engineers at a base automatically attempt to repair any damage existing to their bases, repairing runways first, airfield service damage second and ports last." (p. 214)
Can I create, expand or repair a base without engineers?
No - "Without engineers, bases can’t be created, expanded, or repaired." (p. 249)
Engineers in "combat" OpMode with a destination hex will not build
As noted by SgtSwanson, place in combat mode, but you also cannot have a destination ("Engineers in the hex will help in the building of these fortifications. Engineers will only provide this help if the Engineer is in Combat OpMode and does not have a Destination." p. 198).
[side note] Someone in another thread said that engineers in the DaBabes mod are different.
