Terrified sailors dived for cover in Hamburg, Germany, when what looked like a full-scale U-Boat surfaced on the city's Alster River.
Pranksters caused chaos on the river's Outer Lake with the life-sized replica of a sub conning tower - attached to a pedalo.
Local river police were scrambled after astonished river users dialled 999 to report the lifelike sub, created by pals Marc Aberle 46, Reinhard Crasemann, and Sven-Ole Kramer, both 45.
"It started off as something we might make from a few beer crates but in the end we wanted a complete replica," explained Marc after the maiden voyage of the 'U-Pooly'.
"We didn't think it would cause such a scare, but the police were fine about it - although they said we should have warned them in advance." he added.
The pals took a year working with a local ship-building firm to create the sub and make sure it would not sink on its maiden voyage.
what do you think?
A year to build a conning tower mockup on a pedalo... Pull the other one... I could do that in an afternoon with a little thin plywood or plastic roofing sheeting and some black paint. And the number's 112 not 999 in Europe.
I have come to expect Sky/Orange to be consistent only in their inconsistency and inaccuracy.
I think the name U-POLY on the conning tower rather gives the game away! Very nervous these Germans! Although it looks very realistic, you normally see a fair amount of hull when a submarine surfaces.
The Germans are still very keen untersea specialists. See the very latest developement U212 class hunter killer/attack boats. Diesel electric with 'Air Independant Propulsion' fuel cell. Can cruise undetected for weeks! Just the thing to sink your Atlantic convoys.