This here is a brilliant piece of industrial design: It's functional, durable, makes intelligent and economical use of materials and can easily be mass produced. So successful was the design that it was copied by most major competitors. Most importantly, it's long-lived; the original design was created over 100 years ago, and this object's subsequent iterations are still used and prized today by many.
The object in question is the German mess kit (kochgeschirr) used during World War II. Check out some of its design features, demonstrated here by bushcrafter, hunter and reviewer Virtuovice:
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The sharp-eyed among you may have spotted this slot--which he does not elaborate on--cut into the inner container:
However, we imagine that having the handle be loose made it easy to lose in the field. A subsequent iteration, the Kochgeschirr M1910, cleverly integrated the handle via hinge and designed it to double as the lock-shut latch, as seen in the video above.
Lastly I'll say, I've not seen the locking handle feature shown in the first video in the original German design; I wonder if it's a Japanese upgrade. (By the bye, if any of you cannot understand the first reviewer's accent, list the time code and I'll "translate," as it were.)