very bright light zig-zagging fast across the sky, then zoomed straight up

Very bright light zig-zagged over the ocean in wide sweeping movements, very fast for a few seconds, then zoomed straight up and disappeared.  It had to be a UFO, as there isn't anything else that could travel that swiftly.  The side to side movements were very abrupt and fast---no arcs, just straight lines,  I was on the beach and it was dark so it was very hard to tell how far out over the water this was taking place....maybe 2 miles?? The night was clear--no clouds, no fog, and stars were evident.
Date of incident is approximate.  PD