How was Britain meant to defend Singapore?

How could Britain defend Singapore before the United States entered the war?

Use submarines and prepared regional forces, but the historical plan was hollowed out by diversions to the Mediterranean and North Africa, weak local command, and Japanese access through French Indochina.

Britain's defense plan used T-class submarines to ambush Japanese fleets and forces approaching Singapore. Mediterranean demands drew away submarines, while troops trained for the region went to North Africa and replacements had less familiarity with the terrain. Local priorities favored Malaya's economic role, and the assessment here is sharply critical of the army leadership assigned to its defense. Reinforcements and supplies were expected to travel through the Mediterranean and Suez Canal, or around Africa if necessary, before reaching Singapore through the Indian Ocean. The plan then envisaged operations up the South China Sea. France's defeat and Japanese access to Indochina, together with the collapse of the Philippines, disrupted assumptions about the time available. Whether those plans were adequate is a separate question from what British planners actually intended.