Wrong.50%. A lot of O-4's not yet to the 20 year mark got the "involuntary early retirement" deal in the 90's. It was part of the Peace Dividend of the Clinton era.
It was called Temporary Early Retirement Authority (TERA) and you had to have between 15 and 20 years to be eligible. I took advantage of it the last year it was offered in 1998. It was voluntary (not involuntary) and you had to apply. Acceptance was driven by manning and I know 2 guys (nukes) that were denied. Luckily for me, 1320 LCDRs were plentiful. If you did not apply or were not accepted, you continued to the regular 20 year retirement.
Under TERA, you received all the same benefits as a 20 year retiree. Pay was computed as follows: 2.5% x number of years of service minus 1% for each year less than 20. I retired with 17 years and get 2.5% x 17 - 3% or 39.5%.
The "involuntary" aspect of TERA was that those who were denied continuation to 20 years after 2xFOS had the option to apply for TERA versus getting involuntarily separated with the corresponding lack of any retirement (just separation pay). These guys were automatically accepted to TERA if they applied. Very few Navy 2xFOS were not continued to 20 years by the board. Further, this only really applied to those with 15 to 18 years of service since once you hit 18 years, by law you were entitled to a retirement.
I was 1xFOS when I applied and the Detailer tried to talk me out of it. Supposedly I was going to be the exception and pick up O-5 my second look. The TERA board was 2 weeks before the O-5 board and I was told applying for TERA was an automatic non-select for O-5. So what....I was done. I was at SOUTHCOM hating life with another CVN ship's company tour staring me in the eyes as my final job going to 20 years. It worked great for me, I got to Hawaiian in less than 3 years (not bad for a NFO) during their pre-9/11/2001 expansion.