landing craft. Through the winter of 1943, units jointly developed more advanced assault tactics among the Juno regiments. The landings would be supported by the largest invasion fleet in history – 7,016 vessels in total. The Royal Canadian Navy contributed 121 vessels to the armada, including destroyers, frigates, corvettes, landing ships, minesweepers and torpedo boats. Four Canadian Tribal-class destroyers were in the Royal Navy's 10th Destroyer Flotilla, which joined other RN units in keeping the English Channel near Normandy clear of German naval units. Naval Force J had begun intense training for the invasion with the 3rd Canadian Infantry Division in February 1944, with a full-scale simulation of the invasion carried out on 4 May in Exercise Fabius. On D-Day itself, Force J, commanded from , was to bombard German defensive positions along the landing zone with everything from heavy-calibre cruiser guns to self-propelled artillery attached to landing craft. According to Canadian Army Historian C. P. Stacey, a light bombardment of the landing zone would commence "30 minutes before H Hour and continue for 15 minutes; heavy bombing would then begin on the flanks of the divisional attack, lasting until H Hour". Additional cover would be provided by Royal and Royal Canadian Air Force squadrons both before and on D-Day. A successful surprise invasion required total air superiority over the English Channel and Normandy. In the months preceding D-Day, the RAF Second Tactical Air Force attacked airfields, coastal garrisons, radar, railway lines and transport routes in order to soften the beach defences, as well as prevent the German Luftwaffe from mounting a serious challenge to air superiority over Normandy. By dawn, on 6 June, the RAF tactical air forces had 2,434 fighter and fighter-bomber aircraft with approximately 700 light and medium bombers to support them. The operational plan for Juno was divided into two main sectors: Mike (west) and Nan (east). Mike Sector would be attacked by the 7th Canadian Infantry Brigade, with the Royal Winnipeg Rifles, The Canadian Scottish Regiment and the 1st Hussars in support. The 7th Brigade was to take Courseulles and drive inland. Nan Sector would be assaulted by the Regina Rifle Regiment of 7th Brigade, as well as the North Shore Regiment and the Queen's Own Rifles of Canada of the 8th Canadian Infantry Brigade, while tanks of the Fort Garry Horse provided armoured support; a squadron of specialized Armoured Vehicle Royal Engineers (AVRE) from the British 79th Armoured Division would land on each beach sector as well. The 8th Brigade was to capture Bernières and the western edge of Saint-Aubin, then push south into Normandy. The operational plan also called for the 9th Canadian Infantry Brigade and the Sherbrooke Fusiliers to be deployed to Juno as reinforcements within 4 to 6 hours of the initial assault. By nightfall of D-Day, the 3rd Canadian Infantry Division was slated to have captured the high ground west of Caen, the Bayeux–Caen railway line, and the seaside towns of Courseulles, Bernières, Saint-Aubin and Bény-sur-Mer. D-Day landings Early bombardment Air attacks on Normandy's coastal defences began in earnest on 5 June at 23:30, with RAF Bomber Command units targeting the primary coastal defences. The attack continued until 05:15, with of bombs dropped by 1,136 sorties; this marked the largest attack by Bomber Command in terms of tonnage up to that point in the war. Initial attacks on the Atlantic Wall proved ineffective, with poor weather and visibility making it difficult to accurately hit the bunkers and turrets. The bombing left the defences on Omaha, Gold and Juno virtually intact, yet did not damage Allied landing craft in the Channel