A First World War officer's heartbreaking letters to his wife written while in prisoner of war camps are being released 100 years after he signed up.

Lieutenant Otto Feldman, a Czech officer, left behind two daughters and a pregnant wife to join the Austro-Hungarian army in November 1914. He wouldn't meet his son for six years.

Captured by Russians forces and held in prisoner-of-war camps for four years, the soldier found solace during his "mental torment" by writing diary entries to his wife, Else.

"I feared that I won't find the strength to save myself from spiritual death. Last night the redeeming thought came to me; Write to her!"

However, after four years in Russia, the officer was suffering: "How am I doing? I had better keep quiet about that," he wrote.

"When I tell you about it one day, your flesh will creep."

And just a few months later, he seems to have lost touch with his humanity: "Inside me, I do not feel anything anymore," he wrote.

"I feel hunger, cold, boredom, etc, but … my soul is torn to pieces."

Despite being released in 1918, he was trapped in Russia for two more years as civil war raged.

In July 1920, he was finally able to head home with the newly established Czechoslovak Legion, on a train which the nationalist movement had commandeered.

He wrote at the time: "My little mouse! I am coming!

"I was strong enough to withstand the misery of the past six years, now I fear that I am too weak to be able to bear the happiness of the coming days."

Lieutenant Feldman's letters can be found here: http://ottosdiary.com/