So why did the Federal government choose to build the airport at Tullamarine?
I stumbled across a 1963 Federal Parliamentary report
into the Airport in which was summarised the selection of the site.
Tullamarine was chosen as the best site for several reasons - after the possibility of extensions to Essendon Airport was quickly discounted. Several sites were mooted: Tulla, Wittlesea, Hastings, Port Melbourne (!), Werribee, Laverton, Avalon, and Moorabbin. When they considered flight paths, proximity to Melbourne and lower development costs the choice narowed to Tullamarine or Laverton. Laverton had many disadvantages - it was and still is further from Melbourne, was near to an explosives depot too costly to move, and was already in use for military purposes. Traffic (air?) patterns were also considered and again Tulla was the better choice, being able to be co-ordinated with that of the existing airport at Essendon. The committee considered Laverton’s traffic patterns to be “in conflict” with the pattern for Essendon.
The site chosen was generally rural (and therefore cheap) and had a gently sloping plateau and an excellent site for aviation purposes. It also held better prospects for future extension and less chance for urban encroachment.