Write a question about the following article: Sir Ralph Moore and the Royal Niger Company had planned the attack on the Aros and the Ibini Ukpabi oracle since September 1899 but due to lack of necessary manpower, it was delayed until November 1901. On November 28, Lt. Col. Arthur Forbes Montanaro led 87 officers, 1,550 soldiers and 2,100 carriers in four axes of advance to Arochukwu from Oguta, Akwete, Unwana and Itu on a counter-insurgency campaign. As expected, Aro forces resisted all axes strongly, although they lacked modern weapons. However, Arochukwu was captured on December 28 after four days of fierce battles in and around the city. As a result, the Ibini Ukpabi shrine was allegedly blown up. Battles between British and Aro forces continued throughout the region until spring 1902 when Aro forces were defeated in the last major battle at Bende. The Aro Expedition ended three weeks later.

Question about the article:
How many years were there plans being made to attack the Aros and the Ibini Ukpabi oracle?