Many campaign builders will know that doing the necessary research often takes much more time than building a campaign.
Over the years I found a number of sites with useful background information for mission and campaign builders, ranging from mission reports, lists of aircraft losses, information about the units based at certain airfields, to maps showing the movement of frontlines.
I always try to use reliable information based on official documents and not anecdotal stories written after the war.

Here is a list of sites offering historical information for campaign and mission builder:

United States

Large number of articles about ww2 operations by the US military, often with detailed maps
http://www.ibiblio.org/hyperwar/

US-Army documents written during or after the war on all kinds of topics
http://cgsc.contentdm.oclc.org/cdm/landingpage/collection/p4013coll8

US-Navy department commmuniques December 10, 1941 to May 24, 1945. Includes information about air operations
http://www.ibiblio.org/pha/comms/index.html

USAAF and US-Navy accident and MACR database
http://www.aviationarchaeology.com/src/db.asp

Combat Chronology of the USAAF
http://www.usaaf.net/chron/index.htm

Mustang units on Iwo Jima
http://www.506thfightergroup.org/

Great Britain/Commonwealth

RAF
http://www.raf.mod.uk/history/index.cfm

Fleet Air Arm archive
http://www.fleetairarmarchive.net/

RNZAF
http://nzetc.victoria.ac.nz/tm/scholarly/tei-WH2AirF.html

Japan

Imperial Japanese Army and Navy Air Force
http://www.j-aircraft.com/

Germany

Luftwaffe information
http://www.ww2.dk/

German Army in WW2, with large Luftwaffe section (in German).
http://www.lexikon-der-wehrmacht.de/

Luftwaffe in Norway
http://www.luftwaffe.no/

Aircraft wrecksites in Norway
http://tihlde.org/~ktsorens/flyvrak/index.html

Hungary

Hungarian 101st Fighter Group (in Hungarian)
http://www.pumaszallas.hu/

Soviet Union

Soviet eastern front maps
http://www.armchairgeneral.com/rkkaww2/index.htm

Miscellaneous

Biplanes in WW2
http://surfcity.kund.dalnet.se/

Lots of information concerning fighter aces, for example Luftwaffe claims lists
http://aces.safarikovi.org/

Wrecks and airfields in the Pacific and much more
http://www.pacificwrecks.com/


If you know other useful links, please post them here.

thx, very usefull

there is one that I highly recommend for the United States. It is http://www.fold3.com/ the resources there are absolutely stunning. It does require membership, but for absolute authenticity via diaries and after-action reports, there's none finer.

The general problem with a serious research is there often are differing facts depending
on sources. So i never rely on one source alone. I. e. ww2.dk proofed wrong or
unexact for me in many cases so far. Many facts and details are anyway lost forever, and with the
passing away of the WWII veterans it is getting worse more and more.
I recommend reading well books and joining some WWII discussion boards as well. There are a lot of real experts and the most are really keen to help.
Their knowledge is on newest level - oftenly much newer than any other sources.

ATB
Armin

Armins remarks on the problems of research are absolutely correct. When doing the research for missions and campaigns I am trying to use a methodology that is similar to the way historians work. The most important aspect is source criticism. Never entirely trust a single source, always try to do a countercheck with other sources.
If possible use primary documents (mission reports, photos, official loss and victory claims lists, etc.). When researching an air battle compare the reports written by both sides, that's the only reliable way to find out what really happened. You will almost always find discrepancies, there is often over-claiming when it comes to enemy planes shot down or numbers and types of enemy planes are reported incorrectly.

In the past I have learned to distrust older air war literature, especially the books written before the 1980s. Many authors did not use the methodes I have mentioned above. It's obvious that many of these books were written mostly for entertainment purposes, such books are useless as reliable sources.

I couldn't agree more with either of you, and I'm concerned with what exactly you mean.

So I have a question then. I'm an experimental archaeologist by trade and profession. I pride myself on my research.

for example, fold3.com could be most instrumental on briefings, debriefings, and things like that for a US-based historical campaign.

a campaign builder could then go to the other sources, and discern what really happened. But the after-action reports, guncam videos, and unit pictures, war-diaries etc, at least in my profession are extant primary sources. As good as finding an archaeological find that is definitively 15th Century Gothic armor for example.

What I'm wondering is if you guys are in agreement, or if you're contesting? No harm no foul either and no offense taken by either of you. I'm just wondering if there's something I'm missing in regards to Fold3.com

In our case I would consider all your examples primary sources. Literature based on these sources would be a secondary sources. So I would also consider an analysis like the United States Strategic Bombing Survey a secondary sources.
If you like, you could categorise a book entirely based on secondary sources as tertiary source, but as far as I know this distinction isn't always used in historical sciences.