What are these?

Sonobuoy containers.

After the RAF moved the Nimrod fleet to Lossiemouth and at a surplus sale, a local builders merchant bought some of the containers and hundreds of flying boots!

I was thinking maritime patrol, of some sort, interesting

They are grey plastic and are used as bollards in local car parks.

The square depressions and corresponding extrusions suggest that they are male and female locators for stability in stacking vertically .if the buried end contains a female socket it might fit the recessed top end for longitudinal joining in which case they might fit together to make a temporary wall / barrier possibly to sort of sandbag like contain spillages . or they may be part of an adult lego set !

The buried ends are where the openings are, normally with a plastic screw on cap.

An ex Nav on Nimrods has described them as 'transit" containers, which were discarded when the sonobuoys were loaded on the aircraft.

Some kind of old farm equipment ?