An unusual vehicle safety feature — bumpers filled with water — appeared in the late 1960s. One version was demonstrated at a 1967 Van Nuys news conference. The caption for two photos that appeared in the Sept. 13, 1967, Los Angeles Times reported:
Bumpers filled with water were demonstrated Tuesday at Van Nuys, with 100 spectators on hand. On impact, pressure forces stoppers from water-filler tubes, reducing shock. Manufacturer Rich's Soft Cushion Bumper Co. from Sacramento says the devices are being used by several police departments, the Valley Cab Co.'s fleet of 50 cars and many individuals.
I found this Rich's Safety Water Bumpers video on YouTube.