Just a note that Jerome Fine collected together a set of 24 RT-11 releases
(from V01-15 on a DECtape to V05.07 on an RL02 disk) in the form of a
consolidated CD-ROM image.

You can download the CD-ROM from

http://pdp-11.classiccmp.org/RT-11/dists/RT11DV50.ISO.zip

If you're using SIMH PDP11 you can access distributions from RT-11
partitions on the CD-ROM using a SIMH ini file like -

; File rt11.ini for SIMH PDP11
set cpu 11/70, 4M
set cpu noidle
set throttle 10%

set dz disable
set hk disable
set tm disable

set rq enable
set rq0 cdrom
att rq0 RT11DV50.iso

; This is for copying an install disk to.
; For older versions use DECtape (tc) or RK05 (rk)
set rl enable
set rl0 RL02
att rl0 RT11V57.dsk

boot rq0
; end of rt11.ini

Unzip the CD-ROM from the zip file into an empty directory with the above rt11.ini
and start SIMH PDP11

$ pdp11 rt11.ini

PDP-11 simulator V4.0-0 Current git commit id: 852c0bc1
Disabling XQ
/Users/tony/rt11/rt11.ini-7> att rq0 RT11DV50.iso
RQ0: 'RT11DV50.iso' Contains RT11 partitions
4 valid partitions, Type: V05, Sectors On Disk: 242406
/Users/tony/rt11/rt11.ini-13> att rl0 RT11V57.dsk
RL0: creating new file: RT11V57.dsk
Overwrite last track? [N]Y

RT-11XM V05.03
?LD-W-Unable to update disk copy of LD handler

.TYPE V5USER.TXT
[snip]

Each of the CD-ROM four partitions is available as device DU0:, DU1:,
DU2: and DU3:. There are two files on DU0: called README.1ST and
README.2ND you should examine for instructions and the layout of
the CD-ROM.

For example, to make a bootable RL02 disk containing the RT-11
V05.07 installation kit, copy the disk-image file from DU2:RTV5RL.07
to the RL02 media using -

.copy du2:rtv5rl.07 /file DL0: /dev
DL0:/Copy; Are you sure? Y
Output device is larger; Are you sure? Y

Now you have the installation disk on the RL02 in drive DL0:.

You can now perform an installation by booting this disk - but to do this
you should halt SIMH PDP11 and revise the start-up file to add another
RL02 device (as rl1), and boot from rl0. See the appropriate RT-11
installation guide for details (installation normally requires two additional
RL02 disks - one to make a backup of the installation disk, and the other
to make your working system disk).