Most of the NW Europe tank battles were in the relatively open farmlands of Northern France. Urban development and forests between them would have covered no more than a quarter of the land area. There were lots of hedges which obstructed ground fighting but did nothing to prevent observation from the air - or low-level attacks.
The reason for the steeper attack angle adopted by the planes was simply the weapons used; bombs and RPs rather than guns. With those, the steeper the angle of attack, the more accurate they were (except for some who practised 'skip bombing' from right on the deck).
The 40mm Hurris did indeed see service in Europe. This is from 'Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45':
"The IID was not the only Hurricane to carry the 40 mm S gun. The Hurricane IV, of which over five hundred were built, was introduced in 1943 as a specialised ground attack variant. A more powerful engine enabled more armour to be fitted and it had a "universal wing", designed to take various armament options including the S gun or rocket projectiles (RPs); the changeover could be made by five men in about forty minutes. Most saw service overseas but three squadrons based in England (Nos. 137, 164 and 184) were equipped with this aircraft.
Official British reports during 1943 concerning the effectiveness of the armament options for the Hurricane IV make interesting reading. The 40 mm gun was seen as the precision weapon, usable against smaller targets such as locomotives and tanks, while the RPs were thought to be more effective against shipping. It was recommended that all Hurricane IVs should normally be issued fitted with the S gun, with conversion kits for RPs provided, and that squadrons should employ both variants, with different flights being equipped with RPs or S guns. Operations were conducted by 11 Group over France and against coastal shipping, and both guns and RPs were evidently considered satisfactory.
In June 1943 the RAF's order of preference in weapons for use against tanks was given as: 1st 40 mm S gun; 2nd 20 mm cannon with Mk III AP ammunition; 3rd RP with 25 lb AP head; 4th RP with 60 lb HE head; 5th .50" Browning HMG; 6th 9 lb AT bomb. Only the first three of these were considered to be serious anti-tank weapons. Some comment on these preferences is necessary. The 20 mm AP Mk III, as mentioned in Chapter 1, was a tungsten-cored round of considerable performance which was, in the end, not adopted. The RP with 25 lb AP head could penetrate 70-80 mm, which compensated to some extent for its lack of accuracy. The RP with 60 lb HE head was discounted against tanks as it could only penetrate 25 mm, but this assessment rather underestimated the cataclysmic effect of detonating such a large charge against a tank.
The 9 lb AT bomb, jovially known as "Puffball", used a squash-head rather than a HEAT design and a fighter-bomber was expected to carry twenty-four of them, to be released in one diving pass at low altitude.
Despite the success of similar (but smaller) Soviet and German weapons, Puffball proved unsatisfactory due to sympathetic detonations in mid-air (the explosion of the first hits setting off the others) and significant damage from blast and debris being suffered by the carrying aircraft. The 40 mm S gun, 20 mm AP Mk III and 25 lb AP were all considered capable of dealing with the German Mk IV tank and it seemed that the S gun-equipped Hurricane Mk IV would have a part to play in the forthcoming invasion of Europe. Despite this, all Hurricanes were withdrawn from European service in March 1944, just three months before D-day."
The reason for the Hurri's withdrawal is not stated but I suspect a couple of factors:
1. The S gun was unable to penetrate the Tiger tank and probably the Panther also.
2. The plane was relatively vulnerable to Flak.
The RAF went on playing with powerful anti-tank guns, the 47mm P Gun being tried on a Tempest in 1946.
Tony Williams: Military gun and ammunition
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