In Part 1 of this 2-part series, I described an upcoming "collision" between cavalry and submarines at the Western Front Association AGM and Seminar, March 7-9. That will be a brush between the two military/naval arms in a figurative sense.
But the real thing did happen. In World War I, during the disastrous Gallipoli campaign, British and Australian submarines forced their way through the Dardanelles, wreaking havoc with Turkish naval shipping and transports. On one occasion E-14, under the command of LCdr M. E. Nasmith, drove a steamer aground. While preparing to land a boarding party to blow up the ship, E-14 came under fire from a party of Turkish cavalry. To quote By Guess and By God, "Bullets rained down from above and Nasmith felt for once that discretion was the better part of valour".
Part 1 can be seen here.