light scouts; but, nevertheless, they proved themselves capable
of achieving speeds of 100 miles an hour or more in some cases;
which was faster than the average small machine of 1914.

In one respect the development during the War may perhaps have
proved to be somewhat disappointing, as it might have been
expected that great improvements would be effected in metal
construction, leading almost to the abolition of wooden
structures. Although, however, a good deal of experimental work
was done which resulted in overcoming at any rate the worst of
the difficulties, metal-built machines were little used (except
to a certain extent in Germany) chiefly on account of the need
for rapid production and the danger of delay resulting from
switching over from known and tried methods to experimental
types of construction. The Germans constructed some large
machines, such as the giant Siemens-Schukhert machine, entirely
of metal except for the wing covering, while the Fokker and
Junker firms about the time of the Armistice in 1918 both
produced monoplanes with very deep all-metal wings (including
the covering) which were entirely unstayed externally, depending
for their strength on internal bracing. In Great Britain cable
bracing gave place to a great extent to 'stream-line wires,'
which are steel rods rolled to a more or less oval section,
while tie-rods were also extensively used for the internal
bracing of the wings. Great developments in the economical use
of material were also made in the direction of using built-up
main spars for the wings and interplane struts; spars composed
of a series of layers (or 'laminations') of different pieces of
wood also being used.