I found a copy of Gordon's Khartoum Journal and reading through it ran into this:
(referring to relief forces he suspected were coming up the Nile to relieve him during the siege of Khartoum)
"I cannot too much impress on you that this expedition will not encounter any enemy worth the name in an European sense of the word; the struggle is with the climate and destitution of the country. It is one of time and patience, and of small parties of determined men, backed by native allies, which are got by policy and money. A heavy lumbering column, however strong, is nowhere in this land. Parties of forty or sixty men, swiftly moving about, will do more than any column. If you lose two or three, what of it – it is the chance of war. Native allies above all things, at whatever cost. It is the country of the irregular, not of the regular. If you move in mass you will find no end of difficulties; whereas, if you let detached parties dash out here and there you will spread dismay in the Arab ranks. The time to attack is dawn, or rather before it (this is stale news), but sixty men would put these Arabs to flight just before dawn, which one thousand would not accomplish in daylight. This was always Zebehr's tactics. The reason is that the strength of the Arabs is their horsemen, who do not dare to act in the dark. I do hope you all not drag on that artillery: it can only produce delay and do little good. I can say I owe the defeats in the country to having artillery with me, which delayed me much, and it was the artillery with Hicks which, in my opinion, did for him."
This is an interesting read. It's a mix of personal reflections, advice to people who won't read it, a log of minor events happening during the siege, and his personal feelings about a lot of things. That Gordon has to be one of the most interesting characters in history.