A team of private security guards is being employed by railway chiefs in an attempt to stop attacks on its staff.
The security workers are expected to board some services this week. They are already qualified but Connex is giving them extra training on railway procedures.
The measures have been introduced after conductors threatened to strike unless extra safety measures were introduced immediately.
It follows a spate of attacks on railway staff, particularly on Coastway West services.
Connex employees and members of the Rail, Maritime and Transport union met rail bosses in London on Tuesday to hammer out an agreement.
Managers were told they faced a strike ballot if action was not taken by March 6.
The security guards will operate mainly on services between Brighton and Portsmouth, where staff feel most at risk.
Connex, which refused to reveal how much it is spending on the guards, said it was an interim measure until British Transport Police could fund increased protection. The police are responsible for security on the rail network.
A Connex spokesman said: "We have recruited the security staff to supplement the presence of transport police."
A train driver based at Barnham, a Brighton-based conductor and a member of the platform staff at Bromley South have all been victims of serious assaults.
Connex bosses say they will press for severe fines and compensation payments for staff who are assaulted by passengers.
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