Surgeon Commander Birt has made some useful suggestions concerning the Triservice apparatus . The original Triservice anaesthetic apparatus  was supplied with the Houtonox oxygen regulator (Penlon Ltd, Abingdon, UK). This was a compact and rugged flow regulator with a strong metal casing that was accurate and independent of position. It had two preset flow-rates; 1 l.min−1 minute and 4 l.min−1 being the values chosen for production purposes to conserve precious supplies of oxygen. Houghton showed that supplementation with oxygen at 4 l.min−1 would be likely to raise the inspired oxygen concentration to about 60%. This was over 30 years ago, well before the introduction of the pulse oximeter. Later, Wilson, van Heerden and Leigh  demonstrated that higher levels of inspired oxygen are required for effective pre-oxygenation, and Lowe and McFadzean  quantified this for the Triservice anaesthetic apparatus (44 s of apnoea to 95% saturation after pre-oxygenation using 4 l.min−1 with the Triservice anaesthetic apparatus and 173 s using the Bain breathing attachment). For efficient pre-oxygenation the inspired oxygen concentration should be increased to 100% and Birt has suggested one way to do this. An alternative was proposed earlier by Johnson  who prefilled a 40-litre plastic bag attached to the end of the oxygen reservoir of the Triservice anaesthetic apparatus for pre-oxygenation. This method is effective when the oxygen flow rate is limited as with the Houtonox regulator. However, other pre-oxygenation studies [6–8] have demonstrated that three maximal deep-inspirations are as effective as 3–4 min of normal respiration using pure oxygen. By using a 20-litre bag prefilled with oxygen, effective pre-oxygenation can be achieved using three maximal deep-inspirations assuming a vital capacity of 6 litres.