This B@W war time movie, produced pre 1960 I think, was set in a seaside resort in England. Can’t remember the actors, but I’m sure a couple were big names at the time. I think the plot had to do with spies or enemy agents attempting to demolish a pier somewhat like an older version of Brighton Pier; though why I can’t recall or imagine now. There were scenes of frogmen, maybe even subs under the pier. To be honest, I’m not really sure why this one ‘grabbed me’ enough to make me still wonder about, but something in it had an impact on me when I was a 10/11 yo.