Armed members of elite gendarmerie group, the GIGN, from this weekend, as more and more travellers set off on their summer holidays.

The marshalls will wear plain clothes and be on the lookout for anyone appearing suspicious or anyone acting suspiciously, in a bid to prevent terrorist incidents before they occur.

The term 鈥渢rain marshall鈥� comes from the US term 鈥渁ir marshalls鈥� - American plain clothes police officers that are often stationed as extra security on American civilian flights.

The move for the SNCF network was proposed after that took place on an Amsterdam-Paris Thalys train on August 21, 2015.

Beno卯t Terrier, lieutenant-colonel in the gendarmerie, said: 鈥淭his is a high-level commitment with counter-terrorist units. The objective is to stop an attack as early as possible. Train marshalls can get involved as soon as someone鈥檚 personal safety is threatened; or as soon as a threat appears that could cause an accident, and therefore a serious incident.鈥�

An SNCF security officer said: 鈥淚t is a bit of a new move for us, because the threat from terrorism does not usually make up a big part of our training. But we have brought our [SNCF] know-how in terms of the train and railway environment - which is fairly unusual - and also our knowledge on how to intervene in small spaces. Each of us has our own role, and we are all working together on this mission.鈥�

GIGN agents have been undergoing training to cope with any possible terrorist incidents that could take place on board a train, working with existing SNCF security staff, and will now be travelling on SNCF trains for the duration of the summer holidays.

The intention is to 鈥渂lend in to the group鈥� as much as possible.

GIGN officer Matthieu explained: 鈥淏efore boarding the train we prepare for three or four scenarios, and the objective is to blend in. We might get out a smartphone or a book, or talk to people around us. We will dress and behave differently depending on the train.

鈥淚f we take a train at 8h, filled with engineers or business people, we will dress a certain way, and behave differently to if we are on a train filled with students coming back from holidays. It鈥檚 about adaptability.鈥�

Millions of people are expected to travel across France - both on the railways and the roads - in the coming days and weekends, as school summer holidays begin.

Saturday was classed as on 鈥渙range alert鈥� for traffic, while one million people were expected to travel by train - nationally and internationally - on French rail services over the whole weekend.

Strikes and traffic affected some routes - including a 鈥渟urprise strike鈥� by Eurostar personnel - but most international train services (including the Thalys) were expected to be running normally.