Aerospace and Electronic Systems - August 2019 - 50

Feature Article:

DOI. No. 10.1109/MAES.2019.2927850

ASV Mark I, the First Airborne Maritime Surveillance
Radar
Simon Watts, University College London, London, U.K.

INTRODUCTION
The first work on airborne radar was started in 1937 in the
U.K. at the Bawdsey Research Station, at Bawdsey Manor
in Suffolk, flying from Martlesham Heath. The airborne
radar team was led by Dr. E. G. Bowen and comprised Dr.
A. G. Touch, R. Hanbury-Brown, W. Eastwood, P. A.
Hibberd, S. Jefferson, and K. A. Wood. Much of this early
work is recorded in memoires written by team members
[1]-[3]. It is also recorded in the official history of air to
surface vessel (ASV) development that was published by
the Air Ministry in 1954 [4] and a memorandum written
by Dr. Touch while in the USA in 1945 [5]. In the lead up
to the start of WWII, work on airborne radar had mainly
concentrated on airborne interceptor systems and although
much work had been done on developing techniques, limited progress had been made on developing an operational
ASV system. From about August 1939, as it was becoming clear that war was imminent, it was realized that ASV
would be urgently needed. The initial operational concept
was to use ASV to monitor surface shipping and assist aircraft acting as convoy escorts. There was a strong interest
from both the Royal Air Force (RAF) Coastal Command
and the Royal Navy Fleet Air Arm. Design work for a production system started at the end of August 1939 and only
four months later, in the middle of January 1940, ASV
Mk. I had been fitted to 12 Lockheed Hudson and 12 Short
Sunderland aircraft of Coastal Command. ASV Mk. I was
quite experimental and initially lacked spares, ground test
equipment, and operating manuals. It was also quite unreliable with frequent equipment failures. However, valuable lessons were learned and by the end of 1940 a much
better engineered version, ASV Mk. II, was entering service. The early development and operation of ASV Mk. I
Authors' current address: Simon Watts, University
College London, London WC1E 6BT, U.K., E-mail:
(simon.watts.gb@ieee.org).
Manuscript received April 11, 2019, revised June 12,
2019, and ready for publication July 8, 2019.
Review handled by D. W. O'Hagan.
0885-8985/19/$26.00 ß 2019 IEEE
50

is not well documented in the modern literature, although
some material has been accepted for publication in [6].
The detailed Air Publications (the official Air Ministry
handbooks) and RAF trials assessments of the later versions of ASV developed over the course of the war do not
exist for ASV Mk. I. This paper is an attempt to bring
together what is known of this pioneering system, drawing
on the official files and reports from the time held by the
National Archives of the U.K. and other historical sources.
First, the early technical developments are discussed
and then the ASV Mk. I equipment that entered service at
the start of 1940 is described, together with details of the
installation of the hardware and the aerials on Lockheed
Hudson and Short Sunderland aircraft. The whole concept
of airborne radar and how it should be used would have
been completely new to the users and maintainers at that
time. This paper describes the instructions issued at the
time for operating ASV Mk. I and the performance as
reported by operational squadrons. Finally, there is a brief
introduction to its successor, ASV Mk. II (ASE and SCR521 in the USA). Throughout this paper, free use is made
of the term radar, although this did not enter common use
until 1942. Terms like aerial, rather than antenna, and the
unit of frequency as cycle per second rather than hertz, are
used throughout as they were current when ASV was
being developed and used.

EARLY DEVELOPMENT OF ASV EQUIPMENT
Research had started on ASV during 1938. In his memorandum "Chronological History of Airborne RDF (1936-
1941)" [5], A. G. Touch, a member of Bowen's airborne
radar team, described various approaches that had been
tried. The chosen frequency for early airborne radar systems was around 200 Mc/s. Many different aerial arrangements were tried, including simple dipoles and various
types of side-looking high-gain aerial arrays. A D/F system was developed employing lobe switching between
two forward-looking aerials with overlapping polar diagrams. Initially, this was attempted by using a receiver
with dual RF and video stages, but the two channels

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