Former signallers are being asked to return to the railways across the south of England in a bid to help key workers during the coronavirus crisis.
Network Rail said its southern region "carries half of all passengers in the country" as well as rail freight for the Channel Tunnel.
Bosses want signal boxes and control centres open all day, despite losing staff to self-isolation and sickness.
It said it would provide training for former signallers.
Network Rail said it was already using some of its controllers and local managers, who were also qualified signallers, across its Kent, Sussex and Wessex routes.
'Pressure is on'
A spokesman said there were up to 40 former signallers in the south region - which covers Dorset, Hampshire, Berkshire, Sussex, Surrey, Kent and London - and the firm had already had a "good response".
They were needed for the centres in Basingstoke in Hampshire, Three Bridges in Sussex, and Ashford and Gillingham in Kent, he added.
John Halsall, Network Rail's managing director for the southern region, said: "This region carries half of all passengers in the country and Channel Tunnel rail freight and the pressure is on us to keep that going more than ever before."
"Under normal circumstances we have enough signallers to keep trains running whatever happens, from flu to winter colds season, but these are not normal circumstances and without signallers to route trains there will be no way we can keep the whole network open."
The rail firm said there were currently no forecasted line closures due to Covid-19 in the southern area.
However, on Friday it was announced trains operators across Britain would reduce services from Monday, amid falling demand because of the pandemic.