The key behind Japan's success was Intelligence,
Espionage.
Japanese intelligence & espionage activities were traced as far
back as the 1930s. Malaya was well infiltrated, providing the Japs
with vital information.
Ibrahim bin Haji Ya'acob a journalist for Warta Malaya, cum
recruiter for KMM, passed important information regarding suitable
landing places in Kota bahru, British troop dispositions as well as
locations of fortifications along the Perak River to the
japanese.
Colonel Kadomatsu Tsungunori, worked undercover at the Officer's
Club in Singapore's Naval base, and was speculated to have
discovered the arrival of Prince of Wales, a month before the
Japanese attack came!
Besides gathering of information, the Japanese were able to
manipulate the Indian Independence league to carry out subversive
actions that weakened the force defending singapore signficantly.
Indian troops comprised of 49% of the combined Brit, Oz, Nz,
commonwealth troops defending Singapore.
Operational deception or British folly? Operation Matador was a
plan to strike into Thailand to secure Singora and Patani on the
East Coast of thailand, where the Brits believed the Japanese will
land. British intelligence efforts was centred around Matador, and
troops spent most of their time preparing for it. Unfortunately,
the Japs landed on Kota Bahru as well. Perhaps due to lack of
preparations, the Brits were unable to react and switch to a
defensive posture which pretty much spelt the collapse of the
British front in Northern Malaya.
By the time the Japanese reached Singapore, desertion rate was very
high. Indian army troops were subverted over to the Indian National
Army. An example being the 12th Indian Brigade, within a span of 3
days, it was reduced to just 70 men. High rate of desertion, lack
of air support, poor leadership, inappropriate training, poor
quality of some reinforcements, 2 mths of retreat, absence of
tanks... all contributed to the low troop morale of island
defenders.
IMO, replicating the same conditions, Singapore could not have been
held. Even if Percival had not surrendered totally and officially,
there would have been little fighting instead, individual units
surrendering on their own accord.
Acknowledgements: Far Eastern File by Peter Elphick where most of
the information was researched from.