One in 10 of the infamous Black-and-Tan force which terrorised the Irish population during the War of Independence was an Irish-born Roman Catholic, a new study has shown.

A study of the Tans and Auxiliaries, who joined the Royal Irish Constabulary at the beginning of 1920 when many Royal Irish Constabulary (RIC) men resigned, is set to create controversy among historians.

The study, carried out by W.C. Lowe and published in the current edition of History Ireland, has found that while 78.6 per cent of the Black-and-Tans were British, nearly 19 per cent of them were Irish-born.

"An unexpected finding that is at odds with popular memory is that nearly 19 per cent of the sampled recruits (514) were Irish born, 20 per cent of the Black-and-Tans and about 10 per cent of Auxiliaries," the report states.

The Auxiliaries were former military officers who wore the distinctive Tam o'Shanter caps and operated in counter insurgency units independent of other RIC formations but have been frequently lumped in with the Tans.

"Extrapolating from the sample, more than 2,300 of all Black-and-Tans and 225 of all Auxiliaries were Irish," according to the study.

A breakdown of the religion of the Black-and-Tans and Auxiliaries found that 82 per cent of them were Protestant, 17.4 per cent were Catholic, and there were 10 English Jews.

"The largest proportion of Catholics, not surprisingly, was found among the Irish recruits, that is 59 per cent of the 478 Catholics in the survey," the report continues.

"Fifty five per cent of the Irish recruits were Catholic, mostly concentrated among the Black-and-Tans.

"Those born in Connacht and Muster were overwhelmingly Catholic, 78 per cent and 60 per cent of the Leinstermen were Catholic," it states.

"Ulster born Black-and-Tans were overwhelmingly Protestant (72 per cent) and the 46 Irish Auxiliaries included seventeen Catholics."

The men who joined the ranks of the RIC as irregulars were recruited mainly in England. One-third joined in London, and 36 per cent joined in Liverpool and Glasgow, but nearly 14 per cent of the sample looked at in the survey were recruited in Ireland.

The study finds that 70 per cent of English and 80 per cent of Scottish Black-and-Tans had prior military service, but fewer than 40 per cent of Irish recruits were veterans.

According to the findings, Cork was the most dangerous place for the Black-and Tans, followed by Tipperary.

Prof Lowe is provost and professor of history at Metropolitan State University, St Paul, Minnesota.