Tag Archives: project scheduling

The origins of PERT and CPM – What came before the computers!

The development of PERT and CPM as Mainframe software systems starting in 1957 is well documented with contemporary accounts from the key people involved readily available.  What is less clear is how two systems developed contemporaneously, but in isolation, as well as a number of less well documented similar systems developed in the same timeframe in the UK and Europe came to have so many similar features.  These early tools used the ‘activity-on-arrow’ (AoA or ADM) notation which is a far from obvious model.  Later iterations of the concept of CPM used the ‘precedence’ notation which evolved from the way flow-charts were and are drawn.


One obvious connection between the early developments was the community of interest around Operation (or Operational) Research (OR) a concept developed by the British at the beginning of WW2.  OR had developed to include the concept of linear programming by the mid-1950s which is the mathematical underpinning of CPM, but while this link explains some of the cross pollination of ideas and the mathematics it does not explain terms such as ‘float’ and the AoA notation (for more on the development of CPM as a computer based tool see http://www.mosaicprojects.com.au/PDF_Papers/P042_History%20of%20Scheduing.pdf).

A recent email from Chris Fostel, an Engineering Planning Analyst with Northrop Grumman Corporation (CFostel@rcn.com) appears to offer a rational explanation.  I’ve reproduced Chris’ email pretty much verbatim below – the challenge posed to you is to see if the oral history laid out below can be corroborated or validated.  I look forward to the responses.

Chris’ Oral History

quartermaster_corpsI was told this story in 1978 by a retired quartermaster who founded his own company after the War to utilize his global contacts and planning skills.  Unfortunately the individual who told me this story passed away quite a few years ago and I’m not sure any of his compatriots are still alive either.  Regardless, I thought I should pass this along before I join them in the next life.  I do not wish to minimize the work of Kelly and Walker. They introduced critical path scheduling to the world and formalized the algorithms.  They did not develop or invent the technique.

The origin of critical path scheduling was the planning of the US Pacific Island hopping campaign during World War II.  The Quartermaster Corps coordinated orders to dozens if not hundreds of warships, troop ships and supply ships for each assault on a new island.  If any ships arrived early it would alert the Japanese of an imminent attack.  Surprise was critical to the success of the island hopping campaign.  The US did not have enough warships to fight off the much larger Japanese fleet until late in the war. Alerting the Japanese high command would allow the Japanese fleet to intercept and destroy the slow moving US troop ships before they had a chance to launch an attack. 

Initially the quartermasters drew up their plans on maps of the pacific islands, including current location and travel times of each ship involved.  The travel times were drawn as arrows on the map.  Significant events, personnel or supplies that traveled by air were shown as dashed lines hopping over the ship’s arrows.  The quartermasters would then calculate shortest and longest travel times to the destination for all ships involved in the assault. The plans became very complicated.  Many ships made intermediate stops at various islands to refuel or transfer cargo and personnel.  The goal was to have all ships arrive at the same time.  It didn’t take the quartermasters long to realize that a photograph of the planning maps would be a devastating intelligence lapse.  They started drawing the islands as identical bubbles with identification codes and no particular geographical order on the bubble and arrow charts. These were the first activity on arrow critical path charts; circa 1942. 

The only validation I can offer you is that by now you should realize that activity on arrow diagrams were intuitive as was the term ‘float.’  Float was the amount of time a particular ship could float at anchor before getting underway for the rendezvous.  Later when the US quartermasters introduced the technique to the British for planning the D-Day invasion the British changed float to “Slack”, to broaden the term to include air force and army units which did not float, but could ‘slack off’ for the designated period of time. 

You will not find a written, dated, account of this story by a quartermaster corps veteran.  Critical path scheduling was a military secret until declassification in 1956.  In typical fashion, the veterans of WWII did not write about their experiences during the War.  No one broke the military secrecy.  After 1956 they were free to pass the method on to corporate planners such as Kelly and Walker.  A living WWII Quartermaster veteran, should be able to provide more than my intuitive confirmation.

This narrative makes sense to me from a historical perspective (military planning has involved drawing arrows on maps for at least 200 years) and a timing perspective.  Can we find any additional evidence to back this up??  Over to you!

We are booked to give two presentations

Patrick will be part of the PMI Scheduling CoP’s one day virtual conference Navigating Complexity and De-mystifying Project Scheduling on the 10th July:


His paper Practical project controls – the art of getting to ‘Done’! will be available after presentation. Click to view abstract.

Lynda will be part of the AIPM 2014 Annual Victorian Forum to be held at the National Australia Bank ‘The Arena’ 700 Bourke Street Melbourne 3000 on Thursday 21 August 2014


Her topic is: Doing stakeholder relationship management in South America. For more information download the AIPM event flyer.

Planning Planet Guild Update

After two years of development, the basic framework of the Planning Planet ‘International Guild of Project Controls’ (GPC) is in place to develop a career framework and accreditation system for project controls professionals. The mission of the GPC is to develop a centre of excellence for developing the skills, expertise and capability of professionals in the field of project controls.

The Planning Planet, GPC announcement on the 11/11/11 confirms the Guild’s aims, objectives, governance processes, controls and initial management team are all in place.

The professional development teams are working to establish a framework of ‘standards of practice’ to support project controls professionals in their careers. The current status of this vital work is:

These standards have been mapped to a proposed career framework, and levels of membership, that recognises the different streams of expertise within the overall project controls framework.

With Phase 1 now officially launched, project controls professionals world-wide are invited to become part of the process to define our profession. The first four steps of the process are available now, for you to sign up and support this important development.

Additionally, the schedule leading to the launch of Phase 2 in March 2012 is set out below – if you want to influence this process, now is the time to be involved!!

The launch of Phase 2 will mark the start of formal accreditation to the GPC the intended framework for accreditation has to be finalised but is expected to include the following:

Personally I would like to congratulate James, Theo and the GPC committees on a massive effort and wish them every success as they move forward. If you want to be part of this process or simply find out more, download the GPC Launch presentation and sign up to help at: http://www.planningplanet.com/guild

Assessing Delay and Disruption

In preparation for the IAMA National conference later this week I have just finished developing and updating a short series of papers focused on addressing schedule delay and disruption.

  • Assessing Delay and Disruption – an overview of the accepted methods of forensic schedule analysis [ view the paper ]
  • Prolongation, Disruption and Acceleration Costs – an overview of the options for calculating costs associated with approved delays and acceleration [ view the paper ]
  • The complexities around concurrent and parallel delays are discussed on Mosaic’s White Paper WP1064 Concurrent and Parallel Delays

Any comments are welcome.

Time Analysis Schedule Calculations

There are a range of options for the calculation of dates and float in a CPM network.

I’ve just finished a White Paper focusing on the basic calculations and would appreciate comments on the correctness of the calculations and the methodology adopted.  The aim is to produce a definitive document that is generally agreed. 

You can download the paper from http://www.mosaicprojects.com.au/PDF/Schedule_Calculations.pdf   All comments gratefully appreciated.

Guide to Good Practice in the Management of Time in Complex Projects

Wiley and the Chartered Institute of Building have just published a new book, the Guide to Good Practice in the Management of Time in Complex Projects. The primary purpose of this Guide is to set down the standards necessary to facilitate the effective and competent management of time in complex projects. It defines the standards by which project schedules will be prepared, quality controlled, updated, reviewed and revised in practice and describes the standards of performance which should reasonably be required of a project scheduler.

Delayed completion affects IT, process plant, oil and gas, civil engineering, shipbuilding and marine work contracts. In fact it affects all industries in all countries and the bigger the project, the more damage delayed completion causes to costs, to reputation and sometimes, even to the survival of the contracting parties themselves.

In simple projects, time can be managed intuitively by any reasonably competent person, but complex projects cannot and a more analytical approach is necessary if the project is to succeed. Although much has been written about how to apportion liability for delay after a project has gone wrong there was, until recently, no guidance on how to manage time pro-actively and effectively on complex projects.

The Guide has been developed as a scheduling reference document capable of wide application. It is a practical treatise on the processes to be followed and standards to be achieved in effective management of time. It can be used in any jurisdiction, under any form of contract, with any type of project and should be identified as the required standard for the preparation and updating of contract programmes, progress reporting and time management.

I may be biased, my partner was part of the team that developed The Guide and it recognises the importance of involving stakeholders in the development of the schedule, but I feel it has a lot to offer project planners and schedulers on any type of project.

For more information;
in Australia see: http://www.mosaicprojects.com.au/Books.html#CIOB_Guide elsewhere, http://eu.wiley.com/WileyCDA/WileyTitle/productCd-144433493X.html

PM History papers updated

Working on my paper for PMOZ 2010, Seeing the Road Ahead – the challenge of communicating schedule data  has required me to re-visit two key papers and augment them with new information and materials discovered in the last few years.

A Brief History of Scheduling – Back to the Future has had quite a lot of new materials incorporated. I am now confident this paper accurately lays out the development of scheduling and in particular, the origins of PERT and CPM.

The Origins of Modern Project Management  has had a few new footnotes included an links the development of modern project management to its roots the the spread of scheduling in the early 1960s.

Both updated papers are available for downloading and I have most of the reference materials available for anyone interested in further research into these topics.

The PMOZ paper will be available after publication in a couple of weeks. For more on the PMOZ conference see: http://www.pmoz.com.au/