Although exact figures are tough to come by, a conservative estimate of British troop strength during the Famine (not including local constabularies) is 100,000.  By way of comparison, in 1845-46, the British only maintained about 20,000 troops in the Punjab where they were fighting a Sikh army of 80,000!

The 100,000 troops sent to Ireland were tasked with keeping a mostly impoverished population of 8 million in line – guarding food exports (enough food was being exported from Ireland to feed the starving if it had been kept in country); quelling food riots; and,  protecting the interests of landlords and landed.   Bear in mind that Ireland is roughly 32,000 square miles – the size of Indiana.  With the exception of a very small number of armed men intent on exacting revenge against landlords like Major Mahon who were seen as exploiting the Famine, British troops in Ireland faced a starving, rebellious populace who might riot for food, but posed no military threat.

A point of comparison – the U.S. military maintained roughly 100,000 troops in Afghanistan at the height of that war, a country of over 28 million with a land mass of 250,000 square miles.   Unlike Famine-ravaged Ireland, the U.S. faced a heavily armed Afghan insurgency.

The comparison of these data certainly gives one pause.