s 211 Offenders under 18: detention and training orders
(1) Where— (a) a person aged under 18 is convicted by the Court Martial or the Service Civilian Court of an offence which is punishable with imprisonment in the case of a person aged 21 or over , and (b) the court is of the opinion mentioned in section 260(2) or the case falls within section 260(3), the sentence that the court is to pass is (subject to subsections (2) and (3)) an order that the person shall be subject, for the term specified in the order, to a period of detention and training followed by a period of supervision. (2) In the case of an offender aged under 15 at the time of the conviction, the court may not make an order under this section unless it is of the opinion that he is a persistent offender. (3) In the case of an offender aged under 12 at the time of the conviction, the court may not make an order under this section unless— (a) it is of the opinion mentioned in subsection (2); (b) it is of the opinion that only a custodial sentence would be adequate to protect the public from further offending by him; and (c) the offence was committed after paragraph (aa) of section 234(1) of the Sentencing Code comes into force (see paragraph 27(1)(b) of Schedule 22 to the Sentencing Act 2020). (4) Subsection (1) is also subject to sections 209, 218, ... 221, 221A and 227 (other custodial sentences that may or must be imposed in particular cases).