Today approximately 8,500 men and women serve in the Army. The country is divided into three areas for administrative and operational reasons, and in each area there is an infantry Brigade. The three brigade group structure envisages distinct operational areas of responsibility for each of the brigades.
A Welsh Government can assign the same kind of role to it's Defence Forces as the Irish do:
To defend the State against armed aggression; this being a contingency, preparations for its implementation will depend on an ongoing Government assessment of threats. To aid the Civil Power (meaning in practice to assist, when requested, the Garda Síochána, who have primary responsibility for law and order, including the protection of the internal security of the State). To participate in multinational peace support, crisis management and humanitarian relief operations in support of the United Nations and under UN mandate, including regional security missions authorised by the UN. To provide a fishery protection service in accordance with the State’s obligations as a member of the European Union. To carry out such other duties as may be assigned to them from time to time e.g. search and rescue, air ambulance service, ministerial air transport service, assistance on the occasion of natural or other disasters, assistance in connection with the maintenance of essential services, assistance in combating oil pollution at sea.