After the start of World War I, Crook joined the AIF and served in the 34th Fortress Engineers from November 1915 to October 1916.

To advance his career, Crook decided to gain experience in the United States, setting sail in August 1921.

He gained experience in a number of large electrical engineering firms, including doing drafting work in Chicago, before going to the UK for a year to do a specialised course with Metropolitan-Vickers in Manchester.

In 1929 they built a house in Killara, a dormitory suburb for gentlemen 14 kilometres (about 9 miles) north-west of the Sydney Central Business District.

He returned to Australia with the intention of starting a Rostrum club but was delayed by work commitments, study and marriage.

Freemanship is awarded in recognition of a high level and long standing service to Rostrum and the community At a meeting with two friends, Stuart McPhee, an Electrical Engineer and Fred Seamons, an accountant, in May 1930, Crook explained the objects and methods of The Rostrum club in Manchester.

Robert offered to assist with the formation of Rostrum in Australia and to provide rooms for meetings.

On the evening of 21 July 1930, the seventh anniversary of the formation of The Rostrum club in Manchester, a meeting of 9 people was held at the YMCA.

At the next meeting on the evening of Thursday 28 August 1930, Crook was elected Chief Gardian of Order (Secretary), Robert Swainson, Speaker of the Last Word (Critic / Coach), and John Reaburn, Purseholder (Treasurer).

A constitution was developed in August 1931 allowing for additional clubs with a federated model of zoned centralised state based Daises for their oversight.

Alan Crook was elected Dais secretary, and continued in this role for 36 years until his death in 1965.

As Rostrum clubs grew in number in New South Wales, Crook was present each time for the inaugural meeting.

He traveled to Brisbane on business in 1937, with the resultant meeting agreeing to form a Rostrum Club there on 6 May 1937.

In 1938 on creation of the Federal Rostrum Council, Crook became its secretary and continued in that role until his death 28 years later.

The proposal in 1938 to the NSW Dais to affiliate women's club to Rostrum was strongly opposed by Crook, so the matter was dropped.

On a 1945 business trip that included the United Kingdom, Crook visited Manchester where he was able to attend a special meeting of The Rostrum club and attend their annual pilgrimage to the yew tree at Greendale Farm, Mottram St Andrew, where he addressed the meeting on the success of Rostrum in Australia.

He joined with two Rostrum members to form a club in what was becoming a second business centre for the greater Sydney area.

He substantially recovered, undertook a tour around Australia, spending time on his hobby of photography.

On his return he prepared an illustrated speech titled See Australia First, giving the perspective of a seasoned world traveler.

He was awarded an MBE in the June 1965 Birthday Honours for service to the community, and particularly in recognition of his work in founding Australian Rostrum.