Thieves brought chaos to thousands of early morning rail commuters in Hampshire after stealing 80 metres of copper cabling.
Communications, signalling and trackside controls went down in the Portsmouth area during the outage.
Rail staff later found the cabling coiled and ready for removal in the Hilsea area of the city. It took until mid-morning to replace.
The equipment was only installed last year.
Network Rail said there had been more than 1,000 incidents of copper cable theft in the last year, costing more than £4m.
The copper is melted down and sold on, making it impossible to trace.