### Clue: Posts soldiers to guard heavy artillery, initially two in position (3-5)
### Answer: JOB-SHARE 
 ### Explanation: Definition: two in position
 JOBS(posts/positions in an organisation) + RE(abbrev. for the Royal Engineers in the British army) **containing**(to guard) **1st letters, respectively, of**(…, initially) "heavy artillery".
Defn: Two people each working part-time doing the same job.