This operation was in fact 4 convoys at the same time. One from Gibraltar in the west & one from Alexandria to the east. This was originally to start off in December but was held up due to the activities of the German cruiser Hipper in the Atlantic.
Four merchantmen took part from Gibraltar - three were destined for Piraeus to supply Greek allies & one was bound for Malta carrying 4000 tons of ammunition & 3000 tons of seed potatoes. In Alexandria three merchantmen were assembled - one (an oil tanker, referred to as 'an oiler') was destined for Suda Bay on Crete & 2 other merchantmen carrying oil fuel & petrol destined for Malta. The plan was to get these ships to Malta & escort empty merchantmen back to Alexandria.
Wellington Bombers on the 8th January operating out of Malta (probably Luqa) attacked the Italian Fleet at Naples causing severe damage to the battleship Giulio Cesaere. She & the Vittorio Veneto were hastily withdrawn to Genoa. This action dissuaded Italian surface forces from attacking the convoys.
Two Italian cruisers whilst escorting an Italian supply convoy ran into the British cruiser Bonaventure & the destroyer Hereward. One of the Italian cruisers was sunk with the other escaping damaged. The British destroyer Gallant was damaged by mines off the Italian held island of Pantellaria & had her bows blown off. She was taken in tow by the stern & beached in Malta (where she remained for many years).
On the 9th January the convoy from Gibraltar were attacked by 10 Savoia bombers at high level. The battleship Malaya & the cruiser Gloucester were straddled but not hit. Fulmar fighters were sent after the bombers & shot 2 down.
Meanwhile the Alexandria convoy was under attack at 12.20 by 2 Savoia's carrying torpedo's. The target was the carrier HMS Illustrious which they missed although narrowly missing HMS Valiant. The Fulmar fighter cover dived down against these aircraft & chased them off towards Sicily. This meant the protective fighter umbrella was no longer intact. At 12.30 a large formation of aircraft was observed on radar forming over Sicily. The next Fulmar umbrella was not due to take off from Illustrious until 12.35. Captain Boyd of Illustrious had asked permission of the C in C to turn into the wind to allow the fighters to take off when clearly visible in the distance a black cloud of enemy aircraft could be seen getting closer. In this pack were 40 Ju 87's (Stuka dive bombers) followed by a wave of Ju 88 (bombers). These were part of the crack anti-shipping Fliegerkorps X.
The fleet put up a thick barrage but the German aircrews were regarded as very brave & still came on at 12,000 feet & broke into 2 formations, 30 aircraft attacked Illustrious alone whilst another 10 attacked the battleships. Clearly Illustrious was the prime target. This attack was considered a turning point in the way future sea battles would be fought. The age of the aircraft in an attacking role on warships was born.

An observer quoted - ' We could not but admire the skill & precision of it all. The attacks were pressed home to point-blank range, & as they pulled out of their dives some of them were seen to fly along the flight deck of the Illustrious below the level of her funnel'

A thousand pound bomb flew over the bridge of Admiral Cunningham's flag ship & struck the fluke of the battleship's starboard bow anchor.
Some of these dive bombers attacked at a level of 12,000 feet, others at about half their approach height executed a twist before turning into their bombing dive which was as steep as 80 degrees before putting their air brakes out. This attack commenced at 12.38 & was all over in 6 & a half minutes.
The returning Fulmar fighters tried to gain height as quickly as possibly & shot down 5 dive bombers & harassed the 10 dive bombers making their run on the battleships.
Illustrious had been badly damaged ( at least by 6 x 1000 pounders )& needed to make Malta for extensive repairs. Her steering gear was out of action, bombs had impacted on the lifts used to bring aircraft onto the flight deck, large fires raged through the hold fueled by aviation spirit, 50% of her anti-aircraft 4·5" guns were out of action, fuel tanks & ammunition were exploding all over the ship & the crew suffered heavy casualties. She could however steam at 20 knots as her engines were undamaged. She circled for a time before the rudder amidships was jammed & the revolutions of the engines were varied to steer a course.
A fight to save the ship ensued with stokers in the boiler room fainting through heat exhaustion. The captain decided not to flood the magazines. This was proved a good decision as Savoia bombers attacked from their usual high level but did no damage.
At 1600 hrs 15 Stukas returned this time with an escort of Messerschmitt 109 fighters. Several Stuka's were shot down. One Stuka hit the ship with a thousand pounder which hit the after lift, penetrating through the armour plating to explode inside the ship.
Illustrious was taking water - thousands of tons of water were now inside the ship, fires out of control with many dead & wounded crew aboard. A last attack by torpedo aircraft was beaten off with no damage to the ship.

The merchant ships arrived in Grand Harbour & off loaded their cargoes. At 10 o'clock at night Illustrious was helped into Parlatorio Wharf in French Creek by the paddle tugs.

Operation Excess delivered about 10,000 tons of supplies to Malta.

Ernle Bradford in Siege Malta wrote - 'Smoke still rose from her, she stank of burning cordite, of aviation fuel & oil & blood & tired sweat. So the very face of war was seen in the heart of the island'.

References:
Siege Malta 1940 - 1943. Ernle Bradford. Penguin Books.
Malta Convoys. David A. Thomas