They were for parachute flares used to illuminate the airfield for night landings. They were released by a pull cable running from the cockpit. When pulled the flare would push through a hinged door. In June 1940 the forward tube was either removed or disabled in the Mk I and II due to C of G concerns with the added seat armour. The early Mk V's only had one tube. It was deleted in late production Mk V's and later marks. The flares were about 3 ft long, 4.5 in diameter and weighed about 25 lbs.
Chutes in situ.
When Spitfire Mk I, II and V were modified for the ASR role there was a dinghy survival pack designed that fit in the chute. If the chute had been removed it may have been replaced during the modification.
Dinghy packs being loaded on a Spitfire II ASR.
These shouldn't be confused with the recognition flares originally fired with the Very pistol that was replaced by the Plessy system in June 1940. It was a 6 cartridge downward firing pistol mounted on the lower fuselage centreline positioned about half way between the wing trailing edge and tailplane leading edge. The pilot had a T-handle in the cockpit to select the colour and fire the flare. In April 1941 the pistol was moved to an upward firing position on the right hand side of the spine at about the same fore-aft position. On the later low back marks the port was moved to the left hand side. With the installation of the Plessy system the Very pistol was removed from the cockpit with the seat mounted flare rack remaining for awhile.
The firing port on the spine between the 4 and roundel.
The firing port just aft of the J.
The ports were usually covered with doped fabric. The underside port covering was usually finished to match the underside colour. The spine ports were most often done in red like the gun ports but could be seen in other colours.
The Seafire retained the Very pistol as the original position for the Plessy system was were the arrestor hook was installed.
Cheers,
RichB