Terry Matterson will take charge of the United States side during the World Cup later this year.
The former Castleford coach succeeds Brian Smith, who stepped down on Thursday because of a pressing family engagement.
Matterson, who is currently assistant coach at North Queensland Cowboys, is the Tomahawks’ third head coach in two months after former Bradford boss Matthew Elliott stepped down in August to concentrate on his duties with New Zealand Warriors.
“This is a really good opportunity and I know how good the experience was for Matt Elliott,” said Matterson, who was in charge of Castleford for six seasons between 2006 and 2011.
The Tomahawks are due to play a warm-up match against France in Toulouse on 18 October, before taking on the Cook Islands in the first of their three World Cup group matches on 30 October.
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