The closest alternative would probably have been to immobilise the children by strapping them to a spinal board stretcher, and putting a full face SCUBA mask on

The closest alternative would probably have been to immobilise the children by strapping them to a spinal board stretcher, and putting a full face SCUBA mask on them [and it seems that the other alternative of letting them swim/walk themselves actually worked]. I don't really understand how the more claustrophobic "submarine" capsule would be an improvement on this.