There were a number of issues facing guns on the ‘Strip’ which guns on the ‘Belt’ had not had to deal with:
Air launched missiles could only be safely launched at night.
A constant approach course could not be expected as in the case of bombs launched from ramps.
The possibility of other targets besides London had to be kept in mind, necessitating a wider search arc.
Heights of the flying bombs would vary considerably, with an emphasis on very low heights.
The Diver Gun Strip lay right across the track of bomber aircraft operating from airfields in East Anglia, flying to and from the Continent. Particular care had to be taken with friendly aircraft, which for reasons of operational requirements or distress flew across the Strip from seawards at heights below 4,000 feet.
These peculiarities necessitated more complex rules of engagement than had previously been the case. The general rules of engagement were:
Only flying bombs were to be engaged, NOT hostile aircraft
Only targets within the specified strip (i.e. 5,000 yards inland and 10,000 seawards) were to be engaged.
Targets flying above 5,000 feet were not to be engaged.
The Diver Gun Strip was in force at night only i.e. guns were only permitted to open fire at night. Night was defined as 30 minutes after sunset and 30 minutes before sunrise and these times were broadcast daily as “Night commence” and “Day commence” to the gun sites.
Seen targets could be engaged providing no restriction had been put in place by the Gun Operating Room.
Unseen targets could be engaged only if prior permission had been given by the GOR. The GOR would only give permission to engage unseen targets if permission had been received by 11 Group RAF Controller or “Attack in progress” had been notified by AADC.
HAA and Welter guns were to use Bonzo ammunition only (unless no Bonzo ammunition was available then ammunition with a No 208 fuse was to be used). The use of Bonzo ammunition restricted the arcs at which guns could fire to ensure:
That guns could not fire across land for a distance greater than 7,000 yards from the site
That guns firing seawards could not fire over any arc in which there was inhabited land within 16,000 yards of the site.
Each HAA and Welter site was issued with a permitted arc of fire (known as the Bonzo engagement arc). Further restrictions were in force at some gun sites to prevent bringing down a flying bomb onto, or damage to a Vulnerable Point such as a radar station or over built up areas.
Limitations on the range at which guns could open fire were also in place.
HAA guns could not open fire when the predictor indicated a fuse length beyond 10.
Welter guns could not open fire at a distance greater than 4,000 yards or under 1,000 yards.
40mm guns could not open fire at a range greater than 3,000 yards with predictor No. 10 or 2,000 yards with Predictor No. 3.
By October, engagement rules were modified to allow engagement during the day and also against hostile aircraft. The maximum height that engagement could take place was lowered to 4,000 feet. Unseen aircraft could only be engaged if the order “Attack in progress” had been received. Seen aircraft could only be engaged if clearly recognized as enemy aircraft and observed to bear enemy markings or judged to be hostile by its actions, and its height was below 4,000 feet.
In order to minimize the risk to friendly aircraft, any aircraft that needed to approach the Diver Gun Strip from seawards below 4,000 feet, for whatever reason, was instructed not to approach on a direct line to London (this meant flying on a course as much north of 300˚ as possible) and at a speed not exceeding 285 mph. No target was to be engaged flying on a bearing north of 300˚ unless recognized as a flying bomb.
During the passage of bomber aircraft, 11 Group RAF Controller at Uxbridge could impose restrictions to unseen fire by informing the GORs. To protect other friendly aircraft, the Sector Commander, North Weald or RAF Forward Controllers had absolute power to impose any restrictions as necessary.
Sadly, despite these precautions, some incidents of “friendly fire” did occur. AA Command notes a total of two Mosquitoes and one Boeing being shot down in the Gun Strip during the period to Decemeber. One incident that has been fully documented by Collis & Barker involved a Mosquito from RAF Coltishall which entered the Diver gun Strip while pursing a flying bomb and was brought down in flames at Blundeston by HAA fire on Nov 14th. The aircraft was piloted by two American pilots attached to the RAF to gain night fighter experience and it is probable their inexperience is the reason why they entered the Gun Strip without taking the necessary precautions.
A high state of readiness was required at night when the Diver Gun Strip was in operation. When day time engagement was allowed, no specific state of readiness was specified, guns only opening fire if sufficient personnel were available. Personnel were not to be kept on site for this purpose and personnel resting were not to be disturbed.
The Air War Over Lowestoft, B Collis & S Baker, Lowestoft Aviation Society, 2011