The empire navy : from oak to steel /c [A.J. White & Co. Ltd.].
The pattern
This still is filed under Utility premium.
Define
The free thing is kept because it works (a calendar, a tool, a template) and the brand rides along.
Mechanism
Usefulness as media. Frequency of use is frequency of exposure. Distinct from a keepable card: here the object has a job.
Verdict
We can give something people will actually use next week.
Why it works
It capitalizes on the massive public interest in the British Navy during the naval arms race preceding WWI. By delivering genuinely interesting historical and patriotic content, it ensures the booklet is read and kept.
Steal this when
You want to tie your marketing to a strong current cultural or patriotic interest to increase engagement and retention.