This work sits well within the Irish Historical Monographs series as it takes a fresh look at an issue which has received attention in the past. The subject of Irish troops in Spanish service is not virgin territory, as Brendan Jennings, Wild Geese in Spanish Flanders, 1582–1700 (Dublin, 1964), Gráinne Henry in The Irish military community in Spanish Flanders, 1586–1621 (Dublin, 1992) and Robert A. Stradling, The Spanish monarchy and Irish mercenaries: the Wild Geese in Spain, 1618–68 (Dublin, 1994) covered similar ground. Dr de Mesa, however, delves deeper into the Spanish archive material than his predecessors. The chapters progress logically, beginning with the origins and composition of the Irish tercios, followed by measures used to recruit and transport soldiers out of Ireland. The campaigns of the Irish in Flanders are drawn upon to counter the prevailing views of Spanish military backwardness, whereas the exceptional efforts made by the Spanish to raise new Irish forces are explored with the arrival of two Irish tercios in Spain. Chapters five to seven detail the Irish campaigns in Navarre, Catalonia and Portugal, where they regularly saw action. Lacking reinforcements of fresh Irish recruits, their numbers declined to the point where they were eventually merged into a Spanish tercio.

The author is clear from the start that he has several key goals. He engages with the preoccupation of military revolution theorists with the Dutch and French development of military technology and tactics, which has ignored the role of the Spanish military: indeed, even characterising them as redundant or backwards in comparison to the new trends in Europe. The author explores the importance of the Irish as elite forces within the Spanish army, their favoured position in the Spanish court and the extreme efforts made by those in the Spanish court to maintain and increase the numbers of Irish troops at their disposal. The book is at its strongest when exploring the circuitous and regular, though mainly futile, efforts to raise new levies of troops from Ireland. The Spanish crown took exceptional measures and invested substantial sums of money in these attempts, for relatively meagre returns. Spanish frustration was palpable as successive projects got thwarted by administrative red-tape, both in Spain and abroad, political interference, exaggeration by Irish recruiters or just bad luck. This is where de Mesa’s thorough work in the Spanish archives pays most dividends, as the relationships between the crown, the Irish officers and foreign governments are examined in detail.

De Mesa is less assured dealing with Irish forces in Ireland. He makes presumptions on the capacity for Irish officers to recruit forces by exploiting of bonds of kinship. While there are clearly familial ties in the officer class, there is little to suggest that the common soldiers enrolled along clan lines. Moreover, in chapter four, the author refers to the inability of Irish officers to recruit from traditionally loyal territories, in accordance with Pádraig Lenihan’s findings in Confederate Catholics at war 1641–49 (Cork, 2001), p. 31. The book raises issues which are worthy of deeper inquiry. For instance, the author baulks at some of the less-than-honourable activities of the Irish troops. Throughout there are frequent mentions of fractious relations with civilians and civil authorities but little detail is provided regarding the activities of the Irish or the attitudes of their commanding officers. De Mesa recounts the storming of Cambrils in 1641; the plundering which followed proved ‘most satisfying’ (pp 158–9). No mention, however, is made of the massacre of 700 Catalan prisoners the following day or if the Irish took any part. Emphasis is placed on the elite standing of Irish soldiers, indeed it is raised more than once in the conclusions to chapters, but no investigation is made of how or why they managed to perform so well in combat. Furthermore, the Irish tercios differed in composition to other units as they had a far higher proportion of firearms to pikes, begging the question: are they suitable to examine with regards to Spanish combat tactics if their armament was atypical? The title is slightly misleading as the book only really engages with the period 1622–44. Occasionally, the author takes cheap shots at minor inaccuracies in others’ work for no real gain. His allusion to native Irish warfare as backward until refined in the Spanish school is unhelpful, whereas the suggestion that ties of kinship caused the Irish to falter when their commander was killed at Barcelona, as opposed to a failure in command caused by their loss of a respected officer, groundlessly insinuates latent primitivism within the Irish troops.

Imperfections aside this is an enjoyable and highly detailed work with clearly a substantial amount of time spent in the Spanish archives. De Mesa delivers on his promises and succeeds in showing that the Spanish tercio was more flexible and adaptive than the military revolution theorists would suggest, and that the Irish impact on the battlefield and corresponding reputation was far greater than their small numbers would have suggested, which helps to explain why the Spanish crown was so keen to retain them. However, the author raises as many questions as he solves, though some of these may have been answered but for constraints of space. Nonetheless, the work is a strong foundation for de Mesa and others to build upon.