When the public security is manifestly endangered by any such assembly and when neither the Minister nor the Commissioner of Police nor a Deputy Commissioner of Police can be communicated with, any commissioned officer in the Singapore Armed Forces may disperse such assembly by military force and may arrest and confine the persons forming part of it as it may be necessary to arrest and confine in order to disperse the assembly or to have them punished according to law, but if while he is acting under this section it becomes practicable for him to communicate with the Minister, the Commissioner of Police or a Deputy Commissioner of Police, he shall do so and thereafter obey the instructions of the Minister, the Commissioner of Police or the Deputy Commissioner of Police as to whether he shall or shall not continue the action.