The OTR GroupOpen almost any project schedule and you will meet the idea of a critical path. It feels like a modern planning term, yet it dates back to the late 1950s. This short history explains where it came from, what it means and why it still matters.
A problem at DuPont
The Project Management Institute (PMI) records that DuPont assigned a team led by Morgan Walker to find new ways of scheduling large maintenance projects. Working with James Kelley of Remington Rand, they produced the Critical Path Method, known as CPM, in 1957. It was first described in public literature a couple of years later. Wikipedia adds that DuPont had developed precursors of the critical path between 1940 and 1943, which contributed to the Manhattan Project.
What a critical path is
A critical path is determined by identifying the longest stretch of dependent activities and measuring the time required to complete them from start to finish. Put another way, it is the sequence of project activities that adds up to the longest overall duration. Any delay to an activity on that sequence delays the whole project, which is why project managers watch it closely.
The Navy and PERT
At roughly the same time, the United States Navy's Special Projects Office was working on the Polaris missile programme. PMI notes that a team of researchers was assigned to develop a scheduling technique for it, and the result became the Program Evaluation and Review Technique, or PERT. Sources differ slightly on the date. Wikipedia says PERT was originally developed for the Navy in 1958, while PMI's reference list dates the team's published paper to 1959. The safest summary is that PERT emerged in the late 1950s.
Wikipedia credits the Navy's Special Projects Office, Lockheed Aircraft and Booz Allen Hamilton with supporting the Polaris effort. James Kelley later attributed the term "critical path" to the PERT developers, a reminder that the two techniques grew up side by side.
Why the history matters
- Dependencies come first. Both methods start by mapping which tasks depend on others, not by listing tasks in the order people happen to think of them.
- Duration drives focus. The longest chain of dependent tasks sets the minimum project length, so effort belongs there first.
- Plans are living tools. The original aim was to schedule real, complex work and to update the schedule as conditions changed.
Using the idea today
Modern scheduling software calculates critical paths automatically, but the thinking is still worth doing by hand on a small project. List the tasks, note what each depends on, estimate durations and trace the longest chain. Then ask three questions: which tasks on that chain carry the most uncertainty, who owns them, and what would you do if one slipped?
A caution
A critical path is only as good as the estimates and dependencies behind it. If a dependency is missing, or a task is quietly waiting for a decision nobody has made, the path on paper may not be the path in reality. Review it whenever the plan changes.
This article is general information about project management history. Sources: Project Management Institute, Project network models: past, present, future; Wikipedia entries on the critical path method and PERT.