In his second mission, Heslop was the organiser of the Marksman network (or circuit) assisting one of the largest groups of the French Resistance which operated in the mountainous region near the border with Switzerland.

[6] Heslop applied for the Field Security Police in England in February 1940 and as a corporal took part in an unsuccessful attempt to capture Dakar in Senegal from Vichy France in September 1940.

[8] The three SOE agents spent almost 3 months in miserable, starving conditions in the Castres prison before being transferred on 7 November to an internment camp for captured British soldiers.

Heslop and Wilkinson decided to leave the region as quickly as possible and walked to Le Puy-en-Velay, 160 kilometres (99 miles) distant, where they separated.

Finally in contact with London, he returned to England on the night of 23/24 June 1943 via a Westland Lysander airplane which picked him up at a clandestine airfield near Pocé-sur-Cisse.

Many SOE agents did not survive their first few weeks or months in France, including Heslop's friend Edward Wilkinson who was captured by the Germans in June 1943 and later executed.

Heslop identified three enemies in his region: the German army, the Groupe mobile de réserve (GMR), a semi-trained paramilitary of the Vichy government, and the Milice, a vicious, pro-German militia.

Romans had 1,000 followers in the Ain, mostly young men fleeing their homes to avoid being forced by the Germans to work in factories in Germany.

Heslop traveled around his large area of operations by automobile and truck, risking capture at checkpoints manned by French police.

In early March, Tom Morel, the maquis commander on the Glieres Plateau, was killed in a commando raid on a GMR headquarters.

In early 1944 the impatient and newly-armed maquis were all too eager to take on the German military directly rather than confining themselves to sabotage and guerrilla tactics, as advised by Heslop and the SOE.

These late-comers were called the "Mothball Brigade" (because their military uniforms had been hanging unused in their closets until allied victory became likely) and were shunted aside into units of their own.

[22] Heslop and Roman-Petit's objectives after D-Day were to kill every German and to end all rail transport in their 26,000 square kilometres (10,000 sq mi) area of operations.

He also armed an additional 2,000 men, members of the Armée Secrète which owed allegiance to Charles de Gaulle, who increasingly was taking over leadership of all the different resistance groups.

In the case of Bourg, the allied command had warned that the town would be bombed by air, causing civilian casualties, if the maquis were not able to damage the railyard.

In a bizarre incident in mid-September, Henri Romans-Petit, the commander of the maquis supplied by Heslop, was arrested and imprisoned for a few weeks by the new French government of de Gaulle.