Cue more write-downs, as if there weren’t enough to begin with. Moody’s Investors Service has decided that it’s finally time to downgrade investment grade subprime RMBS — you know, the Aaa-rated stuff? Between Monday and Tuesday, calculations by Housing Wire show that the rating agency has slashed ratings on 1,923 tranches from 232 separate subprime RMBS deals from 2005-2007 vintages. That total includes hundreds of formerly Aaa-rated securities, as Moody’s embarked on its largest round of downgrades to investment grade subprime MBS since the credit crisis began. A little over one month ago, HW covered a Bloomberg special report that suggested that both Standard and Poor’s and Moody’s were holding back on downgrades to the most senior RMBS bonds. Moody’s, at least, is no longer content to hold off. The agency said it downgraded the ratings over increasing delinquency, foreclosure and REO levels, although it did not provide details of the total dollar amount affected. The downgrades surely tally into the multiple of billions worth of subprime debt, and portend additional earnings pain for many market participants — write-downs on the value of RMBS in a portfolio usually aren’t marked up until a downgrade takes place. Calls to Moody’s representatives for comment and clarification on the dollar amount affected were not immediately returned. For the curious, below is the entire list of downgrades issued since Monday morning and through early Tuesday afternoon, along with links to information on each issuer and affected tranche:

• 59 tranches from 7 subprime RMBS transactions issued by Terwin (full list)
• 53 tranches from 10 subprime RMBS transactions issued by Popular (full list)
• 148 tranches from 19 subprime RMBS transactions issued by Soundview, Aaa downgrades to Soundview Home Loan Trust 2007-1, 2007-WMC1 (full list)
• 50 tranches from 6 subprime RMBS transactions issued by Wells Fargo, Aaa downgrades to Wells Fargo Home Equity Asset-Backed Securities 2007-1 Trust, 2007-2 Trust (full list)
• 131 tranches from 15 subprime RMBS transactions issued by HASCO, Aaa downgrades to HSI Asset Securitization Corp. Trust 2006-HE1, 2006-HE2, 2007-HE1, 2007-HE2, 2007-NC1; also Aaa downgrade to HASCO 2006-WMC1 (full list)
• 48 tranches from 5 subprime RMBS transactions issued by SG, Aaa downgrades to SG Mortgage Securities Trust 2006-FRE1, 2006-FRE2, 2006-OPT2, 2007-NC1 (full list)
• 43 tranches from 7 subprime RMBS transactions issued by Saxon (full list)
• 26 tranches from 3 subprime RMBS transactions issued by People’s Choice, Aaa downgrades to People’s Choice PFRMS 2006-1 (full list)
• 9 tranches from 1 subprime RMBS transaction issued by Wachovia (full list)
• 34 tranches from 5 subprime RMBS transactions issued by Accredited (full list)
• 43 tranches from 5 subprime RMBS transactions issued by ABFC (full list)
• 6 tranches from 2 subprime RMBS transactions issued by Aames Mortgage Investment Trust (full list)
• 8 tranches from 1 subprime RMBS transaction issued by Newcastle Mortgage Securities Trust (full list)
• 286 tranches from 30 subprime RMBS transactions issued by First Franklin, includes Aaa downgrades to First Frankline Mortgage Loan Trust 2006-FF11, 2006-FF12, 2006-FF13, 2006-FF14, 2006-FF15, 2006-FF16, 2006-FF17, 2006-FF18, 2006-FF9, 2007-FF1, 2007-FF2; Aaa downgrades also to Merrill Lynch First Franklin Mortgage Loan Trust, 2007-1, 2007-2, 2007-4 (full list)
• 14 tranches from 2 subprime RMBS transactions issued by Park Place (full list)
• 27 tranches from 3 subprime RMBS transactions issued by Aegis (full list)
• 208 tranches from 27 subprime RMBS transactions issued by SABR, includes Aaa downgrades to Securitized Asset Backed Receivables LLC Trust 2006-FR4, 2006-HE1, 2006-HE2, 2006-NC1, 2006-NC3, 2006-WM2, 2006-WM3, 2006-WM4, 2007-BR1, 2007-BR2, 2007-BR3, 2007-BR4, 2007-HE1, 2007-NC1, 2007-NC2 (full list)
• 90 tranches from 12 subprime RMBS transactions issued by SURF, includes Aaa downgrades to Specialty Underwriting and Residential Finance Trust 2006-AB3, 2007-AB1 (full list)
• 220 tranches from 25 subprime RMBS transactions issued by Citigroup Mortgage Loan Trust, includes Aaa downgrades to Citigroup Mortgage Loan Trust 2006-HE3,2006-NC2, 2007-AHL1, 2007-AHL2, 2007-AHL3, 2007-AMC1, 2007-AMC2 (full list)
• 234 tranches from 27 subprime RMBS transactions issued by JP Morgan Mortgage Acquisition Trust, includes Aaa downgrades to J.P. Morgan Mortgage Acquisition Corp. 2006-WMC2, 2006-WMC3, 2006-WMC4, 2007-HE1 (full list)
• 159 tranches from 17 subprime RMBS transactions issued by CSFB Home Equity Asset Trust, including Aaa downgrades to CSFB Home Equity Asset Trust 2006-6, 2006-7, 2006-8, 2007-1, 2007-2 (full list)
• 27 tranches from 3 subprime RMBS transactions issued by GE-WMC, including Aaa downgrades to GE-WMC Asset-Backed Pass-Through Certificates, Series 2006-1 (full list)