I have flight logs for a WW II B-24 navigator who flew with a combat crew in China Burma India. There is a column for number of landings. The entries range from 1 to 5 or 6, mostly 1 or 2. The time can be as long as 8:00 to 10:00 or more. Why is the number of landings recorded? Is that still done today?
Yes, it's still done today, at least in military aviation.
It's to ensure that the undercarriage does not excede the number of landings it has to endure before being checked/overhauled/replaced. Landing an aircraft can typically be the most stressful regime of flight in terms of loading of certain bits of the aircraft, so it is pertinent to log how many times it happens per flight.
I'm not sure if this is specifically a military question or a general question. In general aviation (FAA) you are required to do a certain number of landings every 3 months to stay current. So landings are logged for this reason.
The specific regulation is 14 CFR 61.57 (a) (1), which says (emphasis added):
[…] no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days […]
I am not yet rated for IFR, so I'm not sure on the specifics about IFR currency mentioned in this regulation. The currency for VFR related flight differs from day and night; however, 3 night landings in 90 days will count to keep you current, while 3 day landings will only keep you current for daytime VFR.
A note on military training:
I was able to find this book/article that alludes to the training of navigators during the second world war; on P.585:
Before 1933 instruction in navigation was given only as part of pilot training.
If the individual in question had a military career and joined before '33 he may have been a pilot first and simply continued with the same log book. Why the landings were logged may just be force of habit. Either way its an interesting read on how difficult it was to be a navigator at the time and exactly what it took to become one.
Landing is not the easiest thing on an airframe! It imparts a lot of stress, and everything we build is designed and evaluated by some statistician to endure a certain number of uses + or - some standard deviation that he/she defines. Even the keys on your keyboard are meant to endure a certain number of presses.
Additionally, if you CAN collect data that you suspect may be useful later, why not? You never know when you may want to use it for something you didn't intend to.
Not sure about the navigator though.