Q. I have read a number of articles about pre-WWII ships being rebuilt in some way with increased beam and tonnage

I have not found a resource that explains how pre-WWII ships were rebuilt to

include increased beam and tonnage.  I have found sources, including experts

you might contact directly, to assist you in determining the answer to your

reference question.

The following article addresses the subject of beam vs. ballast

http://www.kastenmarine.com/beam_vs_ballast.htm  and includes links addressing

marine/nautical design followed by a summary that may prove helpful.

 http://www.nsnet.com/ will link you to NSnet-Maritime News and Information.

There is a research and education component on this website that might be

worth exploring.

http://www.boatdesign.net/   offers an extensive array of data on boats,

including a design support service  and an active forum.  The Boat Design

Forum would be an excellent medium for posing your question.  You are likely

to receive a wealth of opinions and maybe even a definitive answer.

The American Society of Naval Engineers website:

https://www.navalengineers.org/aboutasne/Pages/Staff.aspx  offers a staff

directory from which you might mine a contact that can answer your question or

redirect you.

An interesting site that has an extensive archive of documentation on the

construction records of ships and ship/boat builders is:

http://shipbuildinghistory.com/.  Tim Colton is the creator and manager of the

site.  He is also the controversial  President of Maritime Business

Strategies, LLC, a maritime consulting firm.  His email address is available

on the site as well, so if you can't find the information on the site, you

might consider emailing Mr. Colton directly.

The Defense Technical Information Center (DTIC) is a resource of DoD and

government-funded engineering and technical information.  Their URL is:

http://www.dtic/html .

Click

http://www.craftsmanspace.com/free-books/handbook-of-ship-calculations-construction-and-operation.html

and explore the  online version of  "Handbook of Ship Calculations,

Construction and Operation."

The website for Society of Naval Architects & Marine Engineers:

http://www.sname.org/Home/   has egroups and active blogs that might put you

in direct contact with naval architects and enigeers who are able to answer

your questions.

Books that you might investigate include:

Conway's All the World's Fighting Ships

Jane's Naval Construction and Retrofit Markets Jane's Fighting Ships (if your

interest is specificially modern naval vessels)

Elements of Ship Design by R. Munro-Smith

Modern Ships: Elements of their Design, Construction, and Operation by John H.

LaDage

The Design of Merchant Ships and Cost Estimating: a Treatise on Ship Design

and Cost Estimating, Giving Up-to-Date Methods of Arriving at Correct

Proportions, Form and Power to Attain Minimum Capital Cost with Maximum

Service Efficiency by Alexander Kari.

Search terms you might employ when searching Google and other databases:

ship design

nautical design

nautical engineering

naval architecture

ship construction

shipbuilding

vessels, building

boat design

tonnage

beam

I apologize if I have overloaded you with resources when all you really want

is a simple explanation.  Unfortunately, after extensive researching, I did

not find the answer but I hope this helps.  If I can be of further assistance,

please contact us again.