The phrase “put the recruits through” in this context typically refers to the process of training or preparing new members of a group or organization.

Therefore, the option that best conveys the meaning of the underlined portion in the sentence is “train them” 

He was appointed specifically to train the recruits. This implies that his role involves providing the necessary training to the new recruits to prepare them for their roles.

The other options do not fit as well in this context:

• “Assign them to work” (Option A), “assist them at work” (Option D), and “supervise them at work” (Option E) could be part of his responsibilities, but they don’t capture the specific connotation of training or preparation implied by the phrase “put through”.
• “Discipline them” (Option C) suggests enforcing rules and order, which is not the primary intent here.