Wow, my low opinion of Walter Short, just got even lower. The one thing Hawaii was not short of in 1941 was infantry.
There were more than enough troops on Oahu to repel any possible invasion. Indeed Japan did not have close to the amount of sea lift (transports, oilers, etc.) to mount an unopposed invasion of Hawaii. An opposed invasion would have been a slaughter.
Hawaii was vulnerable to a raid and to submarine attacks on shipping. Not an all-out invasion. Those extra troops should have been trained for air-raid warning, or anti-aircraft duty, not ground fighting.